Research On Compression Deformation Texture And Grain Boundary Characteristic Of TLM Titanium Alloy

The grains preferred orientation (texture) of polycrystalline materials affectstrongly the performance of the polycrystalline material anisotropy and thereby directlyaffect the physical and mechanical properties of materials. Therefore, it is veryimportant to understand the texture evolution of materials under different processingconditions, which is helped to optimize the process, predict and improve theperformance of the final product. The structures and properties of grain boundaries ofthe polycrystalline materials strongly influence the moving of grain boundary, thesegregation phenomena of solute atoms in the grain boundary, as well as the mechanicaland physical properties of materials, and so on. So it becomes an important field ofmaterials science study that improves material performance based on the grain boundarycontrol and design. In the process of developed and modified materials, it is essential tooptimization process, controlling the microstructure evolution and texture evolution thatunderstanding the effect of deformation parameters changing on the deformationbehavior of alloy. In this paper, new near beta biomedical titanium alloy TLM (LowModulus Titanium, nominal composition Ti-3Zr-2Sn-3Mo-25Nb) which is the thirdgeneration of biomedical titanium alloys and independent designed and developed byNorthwest Institute for Nonferrous Metal Research in2005is studied in these directionof the grains preferred orientation (texture) and the structures and properties of grainboundaries. It will be the important technical support for the production and researchprocess of TLM biomedical titanium, such as controlling organizational, optimizingprocessing parameters and improving the mechanical properties, that intensivelystudying the deformation mechanism at the condition of cold and hot deformation,analyzing the microstructure and texture evolution, establishing correspondencebetween the deformation parameter and the microstructure structure and texture,researching the distribution characteristics and mechanisms of grain boundaries.Meanwhile, it will be important technical security to improve the compatibility,mechanical compatibility and implant safety, and safeguard its processing performance.The main studying content and results are as follows:Based on the compression tests of room temperature at the different deformationconditions, the deformation mechanism and the evolution of microstructure and textureof solution treatment TLM alloy are studied. The results show that: The deformation mechanism of TLM titanium alloy primarily involves dislocation slip, twinning andstress-induced α" phase transition. At the stage of5%compression deformation, thedeformation texture strength is of the lowest value, and the stress-induced martensite α"phase tends to {220} plane preferred orientation. As the compression reductionincreasing from10%to50%, dislocation slip plays a leading role at the process ofplastic deformation of alloy, the deformation texture of β-phase gather at {111}<110> and {111}<112> orientation, and the orientation density is enhanced as theincreasing of compression reduction. Comparing to the original texture strength, thestrength of deformation texture shows the law of decreasing-increasing-decreasing.The processing map of solution treatment TLM titanium alloy is established at thetest condition. It provides the foundation for optimizing thermal processing parametersthrough establishing processing map, revealing the hot deformation behaviour andanalyzing the microstructure evolution of TLM titanium alloy. The results show that:There is no instability domain of processing map at the test condition. The most peakeffciency domain appears at around the deformation temperature of850℃and thestrain rate of0.01s-1with a peak effciency of36%. In the processing of TLM alloy hotcompression, the mechanism in stability domain is dominated by dynamic recovery(DRV) and dynamic recrystallization (DRX).The texture component and evolution are studied at the different hot deformationcondition. Meanwhile, combining with the microstructure analysis, the mechanism oftexture evolution is clarified. It provides the foundation and technology support for thetechnological modification of TLM titanium alloy based on the texture field. The resultsshow that: As the deformation temperature increasing, the texture intensity of TLMalloy shows the evolution law of increasing at first and then decreasing. Textureintensity is the lowest value and the grain orientation tends to be more randomdistribution at the condition of deformation temperature of850℃. As the strain rateincreasing, the texture intensity of TLM alloy shows the evolution law of gradual rising.As the deformation reduction increasing, the deformation texture intensity shows thelaw of increasing-decreasing-increasing.Based on the compression tests of room temperature at the different deformationconditions in a range of small reduction, the grain boundarydistribution characteristic ofTLM alloy is studied, and the evolutions of grain boundary misorientation angle andspecial grain boundary CSL are revealed. The results show that: With the strain rateincreased by0.001s-1to1s-1and the deformation increased from3%to4%, the grainboundary numbers near3°orientation angle are significantly increased. At the condition of the1s-1strain rate and3%～4.5%deformation, the numbers of Σ29special grainboundaries are significantly increased as the deformation increasing. With thedeformation increased to4.5%, the numbers of Σ3, Σ13and Σ39special grainboundaries are significantly reduced, while the numbers of Σ11and Σ29special grainboundaries are obviously increased.