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   To evaluate the quality of metallurgy of and titanium alloy ingots, the main points are as follows: 1 uniform chemical composition, not only meet the standard requirements of various alloy elements, but also stably control at an optimal level; 2 main impurities ( The content of Fe, O, etc. is controlled in an appropriate range, and other impurities meet the standard requirements; 3 there are no metallurgical defects such as impurities, segregation, pores, cracks, shrinkage holes and looseness in the ingot; 4 the surface of the ingot is smooth, no cold separation, wrinkles, etc. Surface defects, small amount of head shrinkage and high ingot yield; 5 reasonable shape and precise size, suitable for pressure processing requirements, otherwise it will increase process waste and reduce the yield. The metallurgical defects associated with the smelting process are mainly points 3 and 4, namely composition segregation and surface quality. The segregation in titanium alloy mainly includes two types of α segregation and β segregation. During the melting process, the ingot continuously solidifies continuously from the bottom to the top in the crystallizer. The cooling conditions, the shape and depth of the molten pool are not constant, and the partition coefficients of the alloying elements during solidification and crystallization are different. The alloying elements or compounds are segregated in dendritic crystals to form segregation. The degree of segregation and the quality of the raw materials, the particle size, the distribution and partition coefficient of the alloying elements in the electrode, the solidification rate, the falling block during smelting, the depth of the molten pool, the natural and forced motion of the liquid phase, the diffusion, the grain size and the crystal formation. The method is related to many factors, such as the specific operating process such as melting speed and magnetic field stirring. 1. Macro segregation
Although the ingot segregation problem of VAR-smelted titanium alloys is very similar to the segregation problem of molten steel and superalloys, titanium alloys still have their own unique features. The near-alloy and pure titanium have a very small solid-liquid phase interval, and their solidification mode is similar to that of pure metal. Only the solidification mode of the beta alloy and the near beta alloy has a dendritic interface. In addition, when the titanium alloy solidifies, it precipitates as solid solution β crystal grains, and generally does not precipitate the precipitate phase once.
The solidification front of α-alloy, near-α alloy and CPTi is planar, and there is only the possibility of macrosegregation during solidification. In large-section ingots, attention is paid to controlling the macrosegregation of Al and trace elements 0, Fe and Cu. Segregation of Al content is mainly caused by an increase in the loss of Al volatilization caused by a decrease in the melting rate in the feeding stage.
The solidification front of the β alloy and the near β alloy is dendritic, and microscopic segregation between dendrites may occur. Such alloys are less prone to macrosegregation, but beta speckle or ring segregation may occur. The beta plaque is a region with a large number of β stable elements. The reason for the formation of cyclic segregation is that there is a trace amount of solute enrichment in the dendritic solidification front. When the melting speed or power changes, the solidification equilibrium is destroyed to cause a change in the solute content, and at the same time, the solute content in the solidification interface changes. This composition change is generally small, below 10% solute content. Therefore, the width of the ring segregation is also small, generally less than 100-300 um.
2, micro segregation
The α segregation can be further divided into type I segregation and type II segregation. A long time ago, when people used titanium materials, they noticed that there are some α-phase enrichment areas in the material. The hardness of these areas is much higher than the hardness of the matrix. The analysis of these areas shows that the N, O, C content is higher. These defects are called type I defects or hard alpha defects. It is caused by localization of a stable element such as N, O, etc. and formation of nitrides and oxides with titanium. Such compounds are characterized by being hard and brittle. Alpha segregation seriously damages the fatigue strength and plasticity of materials, and is a fatal defect in aircraft engines and the like. The main source of N, O, C is titanium sponge and added waste, or it is welded in the process of making consumable electrodes. The precautionary measures are mainly to strictly control the quality of titanium sponge and improve the vacuum and cleanliness of the consumable electrode welding process.
Type II defects are caused by local enrichment of α-stabilizing elements such as Al. It mainly occurs in the upper part of the ingot, showing a local increase in the Al content, which is also known as a soft alpha defect. The hardness of such defects is usually comparable to the hardness of the matrix, with extensibility, no cracks due to processing, and smaller defects do not affect the mechanical properties. Class II defects are not formed by solidification segregation, and class II segregation cannot be satisfactorily explained by conventional solidification theory. D. W. Tripp et al. believe that it is caused by shrinkage cavities and voids in the ingot. Due to the formation of shrinkage cavities in the hot titanium alloy ingot, there is a small amount of air inside the cavity, and the gas pressure in the cavity is very low. In this case, aluminum (or any alloying element that has a relatively high volatility at high temperatures) quickly evaporates from the surface of the hot cavity metal into the void, and when the dew point is reached, the vapor condenses or simultaneously on the colder surface of the void Condensation. Thus, some surfaces of the void may form an enrichment of aluminum, tin or other readily vaporizable elements, and some surfaces may form a depletion of these elements. The precaution is to extend the feeding time, but this will increase the volatilization loss of these elements, especially when the ingot diameter is large. In order to solve the above contradiction, a method of increasing the element content at the feeding position to compensate for the volatilization loss or appropriately reducing the feeding time may be employed.
3, micro segregation
The α+β two-phase titanium alloy, the β alloy and the near β alloy with high content of stable cerium tend to form β segregation, and the main expression form is the so-called β plaque, which is the local enrichment region of β stable element. The reason for the formation of the beta plaque is that during the solidification process, equiaxed products appear at the front of the columnar crystal. These equiaxed crystal clusters are deposited at the bottom of the liquid molten pool. Due to the different equilibrium distribution coefficients of the solute elements, the liquid melting between the equiaxed clusters The solute element content in the pool is segregated and preserved. The method of reducing the beta plaque can be considered from the following three aspects: first, reducing the size of the ingot to rapidly solidify; second, reducing the content of the beta speckle element, and controlling it to a lower limit than the standard. Third, as long as other conditions permit, the melting speed can be reduced and the bath depth can be minimized.
4. Segregation of alloying elements
The depletion segregation of alloying elements is also known as bright segregation, and the main manifestation is the depletion of alloying elements in the matrix. According to the analysis, the reason for this kind of segregation is mainly related to the excessive particle size of the raw materials, the abnormal blocking of the smelting process, and the improper use of the arc material during welding and smelting. The smelting process parameters and electromagnetic stirring only serve as an auxiliary. For such segregation, measures such as increasing the mechanical strength of the electrode, melting a finished ingot in a single ingot, increasing the number of melting times, etc., and strengthening the process supervision and stabilizing the process system are generally adopted.
Introduce yourself / Introduce myself
« Last post by Edwardos on 30 April 2020, 23:03:35 »

I am a electronic expert who like to make nice things out of steel.
The most challinging will be titanium.

I  joint to learn

Hope to read lot of interresting stuff
Ik ben tijdje weg geweest maar ik heb mijn Kart / Skelter project beetje aangepast ik wil in plaats  van te gaan lassen wil ik met bouten gaan werken. omdat ik het gemakkelijk kan repareren en veranderen voor aanpassing voor div onderdelen,  ;)
Events and meetings / Call for Abstracts for TITANIUM EUROPE 2019 in Vienna
« Last post by JSimpson on 26 November 2018, 21:15:42 »
International Titanium Association (ITA), has issued a “Call for Abstracts” for the 7th annual TITANIUM EUROPE 2019 Conference which will be held the 13-15th May 2019 at the Austria Trend Hotel Savoyen in Vienna, Austria.

TITANIUM EUROPE 2019 is organized and hosted by the International Titanium Association (ITA).  ITA is the global trade association of the world's primary titanium metal producers who together account for over 90% of worldwide titanium production.  Since 1984, ITA’s mission has been to promote and support the use of titanium metal in new and existing applications by connecting the public interested in using titanium with specialists from across the globe who may offer sales and technical assistance.

ITA provides a forum for the exchange of ideas within the industry and educates the public on every aspect of using titanium metal within their design.

TITANIUM EUROPE 2019 delegates are comprised of Delegation is comprised of 400+ high level CEO, President, Director positions who are from over 25 countries in the capacity of producing, fabricating, distributing or providing raw materials in the titanium metal industry.  Exhibition booth spaces are also limited to a total of 60 and are available now for pre-reservation at

The conference organizing committee is seeking presentation abstracts for market oriented and technical papers alike specifically covering the topics of:


·         Commercial Aerospace;

·         Global Ti Market Economic Drivers;

·         Manufacturing Technology;

·         Integrated Supply Chain

·         Military / Defense


Industrial Markets:

·         Forecasting titanium demand in Nuclear, Thermal, Renewable Power,

          Desalination, Process or Automotive;

·         Field Fabrication / Perceptions (Subset: Repair & Refurbishment);

·         Failure Analysis (Subset: Metallography);

·         Corrosion Environment Onshore Vs. Near Shore;

·         Challenges to Titanium Industry from Shipyards;


Advancement in Titanium Powder

·         Metallurgy;

·         Additive Manufacturing;

·         3D Printing



·         Medical

·         Raw Materials / World Supply Trends;

·         Consumer related markets (architectural, sporting goods, etc.);

·         Material Threats to Titanium Industry


Abstract Submission Requirements/Guidelines:   Go to click on “Events”, “TITANIUM EUROPE 2019”, “Call for Abstracts” for complete details.

The Call for Abstracts deadline is February 25, 2019.

Please Visit:

TITANIUM EUROPE 2019 will host 15-minute slide presentations and will not require formal written or peer review white papers from speakers.  Questions may be directed to Jennifer Simpson, ITA 1-303-404-2221 Telephone or Email at
Hobby Projects / Eigenbouw welk materiaal is goed om mee te bouwen ?
« Last post by tom project on 13 October 2018, 19:40:34 »
Hallo ik ben thuis bezig met eigenbouw het voorbeeld is er al beetje te zien maar nu is mijn vraag waar kan ik dit goed mee bouwen er zijn zoveel soorten metalen.. de afmetingen zijn 165 lengte, en breedte van 65, de rechthoekige chassisbalk is 25x50 en de driekhoeken zijn van 25x25, Geef jullie alternatieven maar! :o
Tantalum / How to get the high purity tantalum?
« Last post by Tiarticle on 10 September 2018, 09:15:54 »
Tantalum belongs to the refractory metal group and is widely used as a minor component in alloys. Its chemical properties are excellent, no matter whether it is cold or hot, it does not react with hydrochloric acid, concentrated nitric acid and “Aqua regia”. Its chemical inertness and relatively low price make it a good alternative to platinum. In addition, tantalum is also highly resistant to corrosion, but its corrosion resistance is not due to tantalum itself, but due to the formation of a stable tantalum pentoxide (Ta2O5) protective film on its surface. Tantalum can be used to manufacture evaporation vessels, as well as tubes, rectifiers, and electrolytic capacitors.

Tantalum, always together with the chemically similar niobium, is usually found in the mineral groups of tantalite, columbite and coltan (a mix of columbite and tantalite, though not recognised as a separate mineral species). So, how to get the tantalum of high purity?

1 Tantalum powder can be obtained by metal thermal reduction (sodium thermal reduction) method. The potassium fluotantalate is reduced with sodium metal under an inert atmosphere: K2TaF7 + 5Na-→Ta+5NaF+2KF. The reaction was carried out in a stainless steel tank, and the reaction was quickly completed when the temperature was heated to 900 °C. The powder prepared by this method has irregular grain shape and fine particle size, and is suitable for making tantalum capacitors.

2 The tantalum powder can also be obtained by molten salt electrolysis: a molten salt of a mixture of potassium fluoroantimonate, potassium fluoride and potassium chloride is used as an electrolyte, and tantalum pentoxide (Ta2O5) is dissolved therein and electrolyzed at 750 °C. This method can obtain a bismuth powder having a purity of 99.8 to 99.9%.

3 Tantalum can also be obtained by carbothermal reduction of Ta2O5. The reduction is generally carried out in two steps: first, a mixture of a certain ratio of Ta2O5 and carbon is made into tantalum carbide (TaC) at 1800 to 2000 ° C in a hydrogen atmosphere. Then, TaC and Ta2O5 are prepared into a mixture in a certain ratio, and reduced to tantalum in a vacuum.

4 Tantalum can also be obtained by thermal decomposition or hydrogen reduction of chloride. The dense metal crucible can be prepared by vacuum arc, electron beam, plasma beam melting or powder metallurgy.

Stanford Advanced Materials
Titanium is corrosion-resistant, so everyone usually thinks it is an inert metal. On the contrary, titanium is actually a very active metal. It has a low equilibrium potential and a high degree of thermodynamic corrosion in the medium, but it is actually a lot. Titanium in the medium is very stable, especially titanium can't react with liquid and solid, and it can't be combined. Even Wangshui can't help it. However, titanium reacts very strongly to gas. Titanium likes nitrogen, oxygen and hydrogen. Many gases such as carbon dioxide, water vapor, and methane are combined. This characteristic of titanium, which has a great affinity with gas, is widely used in our lives.

The most common one is the fireworks that are released during the holiday season. The contribution of titanium here is not small. When titanium powder and oxygen are rapidly combined to burn, they can produce intense heat and brilliance. This feature of titanium not only enhances the atmosphere of people's joy, but also can be used in the military. The dazzling light of the signal flare is the combination of titanium and oxygen. In daily lighting, such as the arc lamp, the right amount of titanium is added. The compound can increase its brightness. The strong absorption of titanium's affinity for air removes air and creates a vacuum. For example, using a vacuum pump made of titanium, the air can be pumped clean and free. In the metallurgical industry, adding a small amount of titanium to molten steel can “eat” the gas and impurities inside, can play a good role in deoxidation and nitrogen removal, and can eliminate the harmful effects of sulfur, thereby improving the mechanical properties of steel. And corrosion resistance.

Writing: Lixing Titanium cathy
Titanium production / Titanium plate titanium alloy material introduction
« Last post by Tiarticle on 20 August 2018, 10:52:44 »
Titanium plate for glasses, referred to as glasses plate, is a plate made of titanium material, which is divided into pure titanium glasses plate, titanium alloy glasses plate and memory titanium glasses plate.

Titanium has good corrosion resistance and is similar to platinum, and its mechanical properties are excellent. Used in the glasses frame is light, flexible, corrosion resistant and so on.

However, titanium and titanium alloy glasses are expensive to produce, are highly demanding in buckling, stamping, cutting, and welding, are not easily soldered and plated, and must be completed in a vacuum. Therefore, the price is relatively expensive, and it is only used for medium and high-end frames.

As a new type of eyewear material, titanium metal has been favored by more and more consumers because of its advantages of lightness, corrosion resistance, anti-allergy and high strength. With the development of titanium materials, the processing technology has become more and more mature. There are many kinds of titanium-based frames such as pure titanium, B-titanium and memory titanium. Among them, pure titanium material frame purity requirements of 99.9% (excluding gaskets, screws, stipules and leg sleeves), its logo is called PURETITANIUM, or abbreviated as Ti-P. However, some manufacturers have also carried out the above identification on some non-pure titanium or titanium alloy materials, and the consumers have insufficient discriminating ability for pure titanium frames, resulting in the appearance of frames after consumers wear titanium frames. Rust, skin allergies and other phenomena have harmed the interests of consumers. Here are a few simple ways to identify a pure titanium frame.

1. By hand weight, usually the alloy frame has a specific gravity of about 8.9g/cm3, and the pure titanium frame has a specific gravity of about 4.5g/cm3. Since the titanium material has a weight equivalent to half of the alloy frame, it is lighter by hand. This is one of the easiest ways to distinguish between titanium and non-titanium frames.

2. Observe the welding points of the nose support and the nose support bucket. The welding of pure titanium material is vacuum oxygen-free welding. Here, the welding mark is "step" shape, the welding of alloy material is spot welding, and the welding mark is "slope". "This is one of the effective ways to distinguish between titanium and non-titanium frames."

3. Observe whether there is a gasket at the hinge joint. The pure titanium frame should not directly contact titanium and titanium at the hinge part, otherwise the phenomenon of wrinkling at the joint and poor joint of the temple may occur. Usually, two thin shims are placed in the hinge part of the pure titanium frame to separate the upper and lower hinges. Therefore, checking the presence or absence of a shim at the hinge is also a good way to identify if it is a pure titanium frame.

4. Use a magnet to make a magnetic reaction, loosen the frame hinge as much as possible, and use a magnet to attract it under free-moving conditions. If the temple is shaken under the attraction of the magnet, the frame is not pure titanium, otherwise the mirror is The frame may be a pure titanium frame.

The titanium plates used in the frames are divided into three categories, pure titanium; TC4; and B titanium 15333, pure titanium is divided into soft and hard boards, generally soft boards are slightly more expensive than hard boards, soft boards are generally The hardness is required to be 67--80; it can be stamped, and the hardness of the hard board is generally 90-97; it cannot be stamped and can only be cut by wire. The 15333 titanium material used for high-end glasses frames is difficult to process.

The advantages of β titanium as a spectacle frame and eyeglass frame:

Β-titanium alloy is a titanium material which is delayed in cooling at the zero boundary point of titanium to complete β-particles. Its processing technology is higher than pure titanium, which has better strength, fatigue resistance and environmental resistance than pure titanium and other titanium alloys. Corrosion property, shape plasticity, solid solution state, its elastic modulus is about 80GPa, slightly higher than the elastic modulus of titanium-nickel shape memory alloy (about 60 GPa), it has high elastic recovery force (ie The arch wire has no permanent deformation after bending at a large distance. The hardness is low, it is easy to form, and can be bent or formed into a complicated shape without being broken. The spectacle frame made by the lens compensates for the lack of elasticity of the pure titanium frame, the elasticity and the memory characteristics, and the processing performance and welding of the β titanium alloy are excellent, and the spectacle frame and style made by the spectacle frame are more. A new generation of glasses for making materials. Therefore, the frame of β-titanium alloy is popular in the developed countries such as Europe and the United States as a medium-to-high-end decoration and a fashion. It has been widely used in the production of high-grade titanium frames and wire.

Writing: Lixing Titanium cathy
Titanium and titanium alloys are new structural materials developed in the 1950s. They have a series of advantages such as high strength, low density, non-magnetic and corrosion resistance. They are favored by naval powers and are widely used in the ship field.

As early as 1963, the Soviet Union and Russia began to study the application of titanium alloys in submarines, breaking through the processing and use of a large number of titanium alloys. The proportion and level of titanium alloy used in submarines are among the highest in the world. In addition, Russia also has a research and development production system for titanium alloys for ships, which can produce various titanium alloy materials for ships, such as titanium alloy nT-3B for submarine shells, titanium alloy nT-7M for marine engines, and titanium alloy nT for power plants. -5B and so on. However, due to the production cost of titanium alloys, the Soviet Union/Russia has stopped using titanium alloy pressure-resistant hulls since the construction of the “Akula”-class attack-type nuclear submarines, but titanium alloys are still used in marine equipment or systems.

Unlike Western countries such as the United States and Britain, which mainly use titanium alloys to make submersible pressure-resistant casings, Su/Russia is the only country in the world that uses titanium alloys to build nuclear submarine pressure-resistant casings. According to statistics, from 1963 to the present, the Soviet Union/Russia has built a total of 19 types of 19 titanium alloy submarines. At present, there are only two "Serra"-class attack-type nuclear submarines and one "Typhoon"-class strategic nuclear submarine in service.

The "French" class cruise missile nuclear submarine is the world's first titanium alloy shell structure submarine. This class has only one ship and was commissioned in 1969. The "French" class submarine is mainly used for the performance and function test of titanium alloy submarine. The Soviet Union mastered the manufacture and welding of high-strength titanium alloy hull structure during the design and construction of "French" class submarine, casting and forging of titanium alloy and Manufacturing process for valve parts and other mechanical components. In addition, the boat itself is also a laboratory. The former Soviet Union tested new prototypes of weapons and equipment under real-scale conditions. These specially developed products played an important role in the development of new Soviet/Russian titanium alloy submarines.

The first boat of the "Alpha" attack-type nuclear submarine was commissioned in 1971. The boat used a number of new technologies, especially the use of a large number of alloy materials. The "Alpha" class submarine hull was double-layered with a high-pressure casing and a pressure-resistant casing. Titanium alloy thick plates, titanium alloy thick plates not only have good toughness, but also have high strength, which can resist the shock wave caused by the explosion of deep water bombs. The boat has outstanding depth and high speed, and its safe dive depth is 900m. The maximum underwater speed is 41kn-42kn.

   In addition to the use of titanium alloy in the housing, the "Alpha" submarine also uses a large number of titanium alloy pipes, titanium valves and their titanium alloy fittings, heat exchange plates and pipes, propellers and propeller shafts in power drives (compared to the previous use) The special copper alloy, under the condition of constant speed, the weight is reduced by more than 50%, the service life is more than 5 times that of the copper alloy.) The key components such as the sonar shroud and the torpedo launching system on the submarine use titanium alloy.

The "Mike"-class attack-type nuclear submarine built only one ship and served in the former Soviet Navy in 1988. The boat adopts a double-shell structure, and the external pressure-resistant casing uses a thick plate of titanium alloy material, and the inner and outer casings have a large spacing, and are divided into seven compartments. The reactor on the boat uses a pressurized water reactor, and its engine disk and rotor blades, pipes, valves and fittings, heat exchange plates and pipes are all made of titanium alloy. The navigation system, search radar, sonar (titanium material shroud) are installed on the boat; the weapon system is also significantly increased compared with the "alpha" level. There are 6 torpedo tubes (radiation tubes made of titanium alloy, the strength is improved). The torpedo launch parameters and other performance are greatly improved), so it can launch a variety of weapons such as cruise missiles, anti-submarine missiles and torpedoes, greatly enriching the submarine's attack means and improving the combat effectiveness of the submarine. During the experimental operation, the boat had landed to a depth of 1,250 m, creating a world record for the depth of combat submarines.

  The "Serra" class first boat was commissioned in 1984, and a total of 2 types and 4 ships were built. The "Serra" class adopts a double-shell structure, and the external pressure-resistant casing uses a thick plate of titanium alloy material, and the inner and outer casings have a large spacing. The power plant is a pressurized water reactor and two steam turbines. The engine disk and rotor blades, pipes, valves and fittings, heat exchange plates and pipes are all made of titanium alloy. The navigation system, search radar, sonar (titanium material shroud) are installed on the boat. The propeller and the propeller shaft in the power drive are made of titanium alloy. The weapon system is equipped with 8 pneumatic and hydraulic balanced torpedo launchers. It is a launch tube made of titanium alloy, which can carry multi-type torpedoes, anti-submarine missiles and long-range cruise missiles. It has strong attack capability.

The typhoon-class ballistic missile submarine is the world's largest nuclear submarine. Its first boat was commissioned in 1982. The "Typhoon" class nuclear submarine adopts a double-shell structure, the non-pressure-resistant casing is made of high-strength and low-magnet steel, and the pressure-resistant casing is made of titanium alloy. The "Typhoon" class has a total of 19 cabins, which are viewed from the cross section as "good" type layouts, and titanium alloy materials are used in the main pressure hull, the pressure-resistant central section and the torpedo compartment. The "Typhoon" class's sturdy dual-shell structure allows most of the torpedo's explosive force to be absorbed by the double-shell pressure chamber and the water outside the casing when it is attacked by ordinary torpedoes, thus protecting the hull. In addition, the reactor piping on the boat, engine and rotor blades, valves and their accessories, heat exchange plates, most pipelines, propellers and propeller shafts in power drives, navigation system fixed components, search radar fixed components, sonar The shroud is made of a titanium alloy material.

Titanium alloys have long been widely used in submarine haulage equipment and systems. In addition to the aforementioned Qin alloy hull applications, Su/Russ also uses titanium alloy materials in submarine sonar devices, nuclear power plants, and submarine piping components.

On the titanium alloy pressure-resistant shell submarine, the Soviet Union began to use the titanium alloy pressure-resistant hull from the "Akura"-class attack-type nuclear submarine in service in 1984 (the design time is "Serra" and "Typhoon" After the level), use high-strength steel instead. The current Russian government attaches great importance to the development of the titanium alloy industry. Russia has issued a large number of support policies to save and revive the titanium alloy industry after the collapse of the Soviet Union, forming the world's largest manufacturer and manufacturer of sponge titanium - VSMPO- AVISMA Associates has laid the foundation for the wide application of Russian titanium alloys in submarines.

In addition, in order to ensure that the Russian Navy continues to lead other countries in the field of titanium applications, Russian materials and submarine experts continue to call on the government to develop titanium alloy development plans, while strengthening the research and development of titanium alloy technology, including high-strength titanium with strength greater than 1300MPa. Alloy, high-formability titanium alloy with better welding performance, low-cost titanium alloy material suitable for large-scale applications. With the recovery of Russia's national strength and the breakthrough of the above-mentioned key technologies of titanium alloys, the proportion of titanium alloy materials used in Russian submarines will further increase in the future.

Writing:Lixing Titanium cathy
Titanium machining / Characteristics Influencing Titanium Machinability
« Last post by Tiarticle on 13 August 2018, 10:43:57 »
The fact that titanium sometimes is classified as difficult to machine by traditional methods in part can be explained by the physical, chemical, and mechanical properties of the metal. For example:

    Titanium is a poor conductor of heat. Heat, generated by the cutting action, does not dissipate quickly. Therefore, most of the heat is concentrated on the cutting edge and the tool face.
    Titanium has a strong alloying tendency or chemical reactivity with materials in the cutting tools at tool operating temperatures. This causes galling, welding, and smearing along with rapid destruction of the cutting tool.
    Titanium has a relatively low modulus of elasticity, thereby having more "springiness" than steel. Work has a tendency to move away from the cutting tool unless heavy cuts are maintained or proper backup is employed. Slender parts tend to deflect under tool pressures, causing chatter, tool rubbing, and tolerance problems. Rigidity of the entire system is consequently very important, as is the use of sharp, properly shaped cutting tools.
    Titanium's fatigue properties are strongly influenced by a tendency to surface damage if certain machining techniques are used. Care must be exercised to avoid the loss of surface integrity, especially during grinding. (This characteristic is described in greater detail below.)
    Titanium's work-hardening characteristics are such that titanium alloys demonstrate a complete absence of "built-up edge." Because of the lack of a stationary mass of metal (built-up edge) ahead of the cutting tool, a high shearing angle is formed. This causes a thin chip to contact a relatively small area on the cutting tool face and results in high bearing loads per unit area. The high bearing force, combined with the friction developed by the chip as it rushes over the bearing area, results in a great increase in heat on a very localized portion of the cutting tool. Furthermore, the combination of high bearing forces and heat produces cratering action close to the cutting edge, resulting in rapid tool breakdown.

With respect to titanium's fatigue properties, briefly noted in the above list, the following details are of interest. As stated, loss of surface integrity must be avoided. If this precaution is not observed, a dramatic loss of mechanical behavior (such as fatigue) can result. Even proper grinding practices using conventional parameters (wheel speed, downfeed, etc.) may result in appreciably lower fatigue strength due to surface damage. The basic fatigue properties of many titanium alloys rely on a favorable compressive surface stress induced by tool action during machining. Electromechanical removal of material, producing a stress-free surface, can cause a debit from the customary design fatigue strength properties. (These results are similar when mechanical processes such as grinding are involved, although the reasons are different.)

Writing: Lixing Titanium cathy
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