Friction properties of titanium alloy materials for artificial joints

Titanium is corrosion-resistant, has high strength and good toughness, and has good enough biocompatibility compared to other metal materials, making it a better choice for artificial joint implants. However, the follow-up study found that the wear resistance of titanium alloys was relatively general, and a small number of patients were allergic to them. Some studies have compared the friction experiments of stainless steel and titanium alloy with alumina under seawater conditions and found that the friction performance of titanium alloy is better than that of stainless steel material in a complex environment, and the friction coefficient is much lower than that of stainless steel material. 316L stainless steel under this condition The friction coefficient is about 0.4-0.6, while the friction coefficient of titanium alloy material is 0.2-0.3. However, ASTM F67 Gr2 Titanium Plate materials have the same phenomenon of corrosion and friction synergy as stainless steel materials, and titanium alloy materials are more serious. In the experiment, the volume loss due to corrosion and friction is more than that of stainless steel materials, but it can be improved by surface treatment technology. The friction and wear properties of titanium alloys enhance wear resistance and reduce the friction coefficient.

A study on the Ni-P coating on the surface of Ultra-Thin Titanium Alloy Sheet found that the friction coefficient of the untreated titanium surface is around 0.6 and fluctuates greatly, and the friction coefficient after the Ni-P coating is basically stable at 0.45. In addition, the effect of depositing TiAlN coating on the surface of titanium alloy by magnetron sputtering is obvious. The wear amount of the TiAlN coating sample is only 20% of that of the titanium alloy substrate. Some domestic scholars have also found that the Al2O3/TiO2 composite nanocoating has better wear resistance. In addition, titanium alloys also have other disadvantages: because the surface hardness of titanium alloys is not high enough, the protection effect of surface oxides is poor, and the mechanical properties are poor, so the friction and wear performance are average. Fortunately, there is much research on titanium alloys. In recent years, new β-titanium alloys have come out. These titanium alloys have lower elastic modulus and better biocompatibility, and the general development trend is good. Titanium alloys have a large market as artificial joint materials, and the research progress is considerable. There is still room for improvement in friction and wear performance.

Empty titanium bar rolling

Heating characteristics and hot rolling characteristics of bars for die forging blades and fasteners. The batch materials used in the manufacture of aviation blades in the former Soviet Union are titanium alloy bars such as BT3-1, BT8, BT9, and OT4 with a diameter of 10-60mm. The material for aviation fasteners generally uses BT16 Titanium Industrial Rod with a diameter of 4.0-16mm.

The heating characteristics and hot rolling characteristics of BT3-1, BT8, BT9, and OT4 alloys determine the requirements for bar quality. For example, when the alloy is hot rolled at the temperature of the ot+p phase region, if its deformation is not less than 40%-50%, then the plasticity and fatigue strength indicators of this material are the highest. However, Grade 2 Pure Titanium Sheet at this temperature can significantly increase the deformation resistance of the billet pass and the intermediate pass, increase the unit pressure, and overload the motor of the rolling mill.

In this case, the rolling process should be carried out in two stages:

(1) Pre-emulsification at a temperature higher than a +p—P transition;

(2) Rolling to finished size at the temperature of the hot +P phase region of the alloy. In the final rolling stage, the rolled material should be cooled to a temperature below 650T.

Bars with a diameter greater than 8.0mm, and restocking of bars with a diameter of 4.0-8.0mm, should be rolled under one fire.

Application of titanium alloy parts in automobile manufacturing

Titanium alloy materials have been widely used in aerospace, petrochemical and shipbuilding industries, but their application in the automotive industry has developed slowly. Starting from the successful development of the first all-titanium car by General Motors in 1956, titanium auto parts did not reach the mass production level until the 1980s. In the 1990s, with the increasing demand for luxury cars, sports cars and racing cars, titanium Manufacturing parts have been developed rapidly. In 1990, the amount of titanium used in automobiles in the world was only 50t, in 1997 it reached 500t, in 2002 it reached 1100t, and in 2009 it reached 3000t. Titanium alloy parts have the following main applications in the automotive industry: titanium square pipe     ERTi-23 Titanium Welding Wire     ASTM F67 Gr2 Titanium Plate     Gr9 Titanium Seamless Tubes For Bike Frame

1. Engine connecting rod

Titanium alloys are ideal materials for connecting rods. The engine connecting rod made of titanium alloy can effectively reduce the quality of the engine, improve the fuel efficiency and reduce the displacement. Compared with steel connecting rods, titanium connecting rods can reduce the mass by 15% to 20%. The materials used for titanium alloy connecting rods are mainly Ti-6Al-4V, Ti-10V-2Fe-3Al, Ti-3Al-2.0V and Ti-4Al-4Mo-Sn-0.5Si, etc. Other titanium alloy materials such as Ti The applications of -4Al-2S i-4Mn and Ti-7M-4Mo in connecting rods are also under development.

2. Engine valve

The automobile engine valve made of titanium alloy can not only reduce the quality and prolong the service life, but also reduce the fuel consumption and improve the reliability of the automobile. Compared with steel valves, titanium valves can reduce the mass by 30% to 40%, and the limit speed of the engine can be increased by 20%. As far as the current application is concerned, the material of the intake valve is mainly Ti-6A l-4V, and the material of the exhaust valve is mainly Ti-6242S. Usually, Sn and Al are added together, which can obtain lower brittleness and better performance. High strength; the addition of Mo can improve the heat treatment performance of titanium alloy, strengthen the strength of quenching and aging titanium alloy, and increase the hardness at the same time.

3. Valve spring seat

High strength and fatigue resistance are the properties that the valve spring seat must have. β-titanium alloy is a heat-treated alloy, which can obtain high strength through solution aging treatment. The corresponding more suitable materials are Ti·15V-3Cr- 3Al-3Sn and Ti-15Mo-3Al-2.7Nb-0.2Si. Mitsubishi Motors uses Ti-22V-4Al titanium alloy valve spring seat in its large-scale production vehicles, which reduces the mass by 42% compared with the original steel lock, reduces the inertial mass of the valve mechanism by 6%, and increases the maximum engine speed. 300r/min.

Method for selecting rolling temperature of industrial titanium plate and titanium alloy plate

Hot rolling of titanium alloy materials should generally be carried out in the B or a+P phase region. The hot rolling temperature is 50~100℃ higher than the forging temperature line, and the plate with a thickness of 2~5mm can use the warm rolling process, and the thinner plate can be cold rolled. During cold rolling, the cold rolling deformation between two anneals is 15% to 60%. Grade 7 Titanium Sheet are metals with phase transformation. The selection of slab heating temperature must consider the process plasticity, deformation resistance of the a+β phase region and the effect of the getter layer on the surface plasticity of the rolled piece at high temperature. The process plasticity of the B-phase region is better than that of the a-phase region, and the deformation resistance is lower, but the heating temperature is high, which increases the depth of the getter layer, and serious cracks will occur on the surface during uneven deformation.

The hot rolling of the titanium plate is carried out in the phase zone, which can ensure good process plasticity, and the total processing rate of the billet can reach 90%. Pure titanium TA1, TA2 and TA3 are below the phase transition point, generally heated at 850~870℃, while TC4 should be selected at the upper limit of the a+B phase transition point or by superplastic forming process (heated at 1000~950℃). TC1, TC2, TC3, etc., the hot rolling process plasticity is slightly worse, the thicker the slab, the more serious the edge cracking and the more serious surface cracking due to uneven deformation during rolling. Although Grade 9 Ti-3Al-2.5V Titanium Plate has good oxidation resistance, it has a high degree of alloying and high deformation resistance. Therefore, selecting the heating temperature of TA7 thick slab in the B phase region is more conducive to deformation, which can make full use of the plasticity of the alloy and reduce the number of tempering.

Advantages of hot die forging and conventional forging of titanium alloys

Like isothermal forging, hot die forging of titanium alloy processing technology is also a promising precision forging process. The difference is that the die temperature of hot die forging is higher than that of ordinary forging, but lower than that of isothermal forging. A typical hot die forging die temperature is 110-225°C lower than the billet temperature. Compared with isothermal forging, the reduction of mold temperature allows a wider selection of mold materials, but the ability to form very thin and complex shape forgings is slightly worse.

Compared with conventional forging, hot die forging has the following advantages:

(1) Reduce the material consumption of titanium forged disc. During hot die forging, the chilling of the die contacting the blank and the work hardening of the material are reduced, and the forgeability of the material is improved, so the forgings are allowed to have a smaller fillet radius and a smaller draft. Slope and small forging allowance, thus greatly reducing the quality of the forging. For example, a Ti-6Al-4V alloy structural part has a mass of 28kg, the mass of the forging produced by the conventional forging process is 154kg, and the mass of the forging produced by the hot die forging process is 109kg, and the difference between the two methods is 45kg.

(2) Reduce the number of forging operations and improve the working capacity of the press. During hot die forging, the temperature of the die is higher and the temperature drop of the billet is less. Conventional Titanium Eye Bolt requires two, three or more fires to form forgings, hot die forging Just one time, as many as two fires can be completed. And due to hot die forging, the deformation resistance of the metal is relatively low, which relatively increases the working capacity of the equipment.

(3) Reduce the amount of machining of forgings Because the produced forgings are close to the weight and contour size of the parts, the amount of material removed in machining is reduced compared to forgings produced by conventional forging.

(4) The uniformity of the product is better. During the forging process, the temperature gradient is greatly reduced, and the uneven deformation caused by the temperature gradient is easily reduced. Therefore, the uniformity and consistency of the structure and performance of the product are better than those produced by conventional forging. , but not as good as forgings produced by isothermal forging.

During hot die forging, although the billet has a temperature drop, it is still in the forging temperature range, and the increase in deformation resistance is not as sharp as in conventional forging. The strain rate used in hot die forging varies in the range of 0.05 to 0.2s-1. If the strain rate is too low, the billet temperature may decrease.

In the hot die forging of titanium alloys, the forging heating temperature, strain rate, microstructure of the preform and holding time are extremely important factors, which play a decisive role in the dimensional accuracy and microstructure of the formed parts. Typically lower strain rates and longer dwell times increase the likelihood of precision forming. The microstructure of the preform has a direct impact on the flow stress and superplasticity of the material, especially the post-forging structure. It is impossible to completely eliminate the defects and grain inhomogeneity in the raw material by isothermal forging or hot die forging.

At present, the use of hot die forging process for titanium alloys and superalloys mainly depends on the total cost of forgings or the needs of product uniformity and consistency. The trend in this process is to use conventional forging preforms, followed by final isothermal or hot die forging.

Performance characteristics and specific applications of titanium alloy materials

The outstanding performance characteristic of titanium alloy material is that its own strength is very high, it can withstand the pressure of 1500 MPa, and the density is only 4.5g/cm3. Secondly, titanium alloy materials have good thermal stability at 300~500 ° C, and their strength is greater than 10 times or even more than common aluminum alloy materials. Thirdly, AMS 4928 Titanium Alloy Bar have strong corrosion resistance, and they are more excellent than stainless steel materials in terms of corrosion resistance, acid corrosion and stress corrosion resistance when exposed to high air humidity and alkaline medium for a long time. The chemical activity of titanium alloy is relatively prominent. After contacting with the material elements such as O2, CO2 and H in the air, it can form a strong chemical reaction. When heated to 600 °C, it will show a violent oxygen absorption characteristic, resulting in a hardness Very high hardened layer. Gr5 Ti-6Al-4V Titanium Foil has poor thermal conductivity, and its thermal conductivity is also relatively low, only 1/5 of iron and 1/4 of nickel. The thermal conductivity of titanium alloy materials is even lower, which is only 1/2 of the thermal conductivity of pure titanium.

Characteristics of titanium alloy materials such as titanium rods and titanium alloy rods and types of heat treatment processes for rods

Titanium is very stable in the air at room temperature. When heated to 400-550 °C, a firm oxide film is formed on the surface, which plays a protective role to prevent further oxidation. Titanium has a strong ability to absorb oxygen, nitrogen, and hydrogen. These gases are impurities that are very harmful to metal titanium, and even a small content (0.01% to 0.005%) can seriously affect its mechanical properties. Among the titanium compounds, titanium dioxide (TiO2) has practical value. TiO2 is inert to the human body, non-toxic, and has a series of excellent optical properties. TiO2 is opaque, with high gloss and whiteness, high refractive index and scattering power, strong covering power, and good dispersibility. The pigment made is a white powder, commonly known as titanium dioxide, which is widely used. The appearance of the machined titanium round rod is very similar to that of steel, with a density of 4.51 g/cm3, which is less than 60% of that of steel, and is a metal element with low density in refractory metals. The mechanical properties of titanium, commonly known as mechanical properties, are closely related to purity. High-purity titanium has excellent machinability, good elongation, and area shrinkage, but low strength and is not suitable for structural materials. Industrial pure titanium contains an appropriate amount of impurities, has high strength and plasticity, and is suitable for making structural materials.

Titanium alloys are divided into low-strength and high-plasticity, medium-strength, and high-strength, ranging from 200 (low-strength) to 1300 (high-strength) MPa, but in general, titanium alloys can be regarded as high-strength alloys. They are stronger than aluminum alloys, which are considered medium-strength, and can completely replace certain types of steel in strength. Some titanium alloys can still maintain good strength at 600°C compared to aluminum alloys whose strength decreases rapidly at temperatures above 150°C. Dense metal titanium is highly valued by the aviation industry due to its lightweight, higher strength than aluminum alloys, and its ability to maintain higher strength than aluminum at high temperatures. Considering that the density of titanium is 57% of that of steel, its specific strength (strength/weight ratio or strength/density ratio) is high, and its anti-corrosion, anti-oxidation, and anti-fatigue capabilities are all strong, and 3/4 of titanium alloys are used as 1/4 of the structural materials represented by aviation structural alloys are mainly used as corrosion-resistant alloys. Titanium alloy has high strength and low density, good mechanical properties, good toughness, and corrosion resistance. In addition, the process performance of titanium alloy is poor, cutting is difficult, and it is very easy to absorb impurities such as hydrogen, oxygen, nitrogen, and carbon during hot processing. There is also poor wear resistance and a complex production process. The industrial production of titanium started in 1948. The need for the development of the aviation industry makes the titanium industry develop at an average annual growth rate of about 8%. At present, the annual output of titanium alloy processing materials in the world has reached more than 40,000 tons, and there are nearly 30 kinds of titanium alloy grades. The widely used titanium alloys are Ti-6Al-4V(TC4)'Ti-5Al-2.5Sn(TA7) and industrial pure titanium (TA1, TA2, and TA3).

There are three heat treatment processes for astm b348 titanium rod and titanium alloy rods:

1. Solution treatment and aging:

The purpose is to increase its strength, alpha titanium alloys and stable beta titanium alloys cannot be strengthened by heat treatment, and are only annealed in production. α+β titanium alloys and metastable β titanium alloys containing a small amount of α phase can be further strengthened by solution treatment and aging.

2. Stress relief annealing:

The purpose is to eliminate or reduce the residual stress generated during processing. Prevent chemical attacks and reduce deformation in some corrosive environments.

3. Complete annealing:

The purpose is to obtain good toughness, improve processing properties, facilitate reprocessing and improve dimensional and organizational stability.