【摘要】 作为一种新型合金，Ti-6Al-4V-0.1B合金显示了较好的塑性成形能力及应用前景。通过真空感应凝壳熔炼方法制备了Ti-6Al-4V-0.1B合金铸锭，随后在850～985℃的温度范围内和0.001～1 s^-1的应变速率范围内对Ti-6Al-4V-0.1B合金进行热压缩测试。运用真应力-真应变曲线研究了合金的流动行为。利用光学显微镜（OM）、扫描电镜（SEM）和电子背散射衍射技术（EBSD）对合金显微组织进行了表征。研究结果显示，Ti-6Al-4V-0.1B合金的流动应力对温度和应变速率都是敏感的，且温度对流动应力的影响比应变速率大。与基体合金相比，Ti-6Al-4V-0.1B合金具有更高的应力指数和应变激活能，这归因于分布在晶界处的TiB增加了原子扩散的阻力，减慢了热变形动态软化过程。热压缩过程中，初生α相发生了明显的球化，球化过程也受变形温度和应变速率的影响。由于TiB与基体之间的应变不匹配导致了高应变速率下合金基体的开裂，随后裂纹沿着定向排列的TiB粒子扩展，因此Ti-6Al-4V-0.1B合金的热加工过程应在低应变速率下进行。更多还原

【Abstract】 Ti-6Al-4V alloy has a small thermal conductivity,and its ingot grains are usually very coarse.The addition of a trace amount of B （0.1%,mass fraction） during the smelting process significantly refines the grains of Ti-6Al-4V through the constitutional undercooling mechanism.B element is distributed in the grain boundary in the form of Ti B particles.Therefore,Ti-6Al-4V-0.1B alloy shows the possibility of direct plastic forming without the cogging process.In order to evaluate the influence of hot working process pa-rameters on alloy high temperature deformation,the deformation behavior of as-cast Ti-6Al-4V-0.1B alloy in different temperature and strain rate ranges was studied.The Ti-6Al-4V-0.1B alloy ingot was prepared by vacuum induction skull melting method,and 16 speci-mens ofΦ8 mm×13 mm were cut at a distance of 30 mm from the upper surface of the ingot using wire-electrode cutting technology.Subsequently,the alloy was subjected to hot compression test in the temperature range of 850～985℃and the strain rate range of 0.001～1 s^-1.The true stress-true strain curve was used to study the flow behavior of the alloy.The research results showed that the flow stress of Ti-6Al-4V-0.1B alloy was sensitive to temperature and strain rate,and temperature had a greater influence on flow stress than strain rate.At a given strain rate,the flow stress of Ti-6Al-4V-0.1B alloy decreased with the increase of temperature;while at a given temperature,the flow stress increased with the increase of strain rate.Under the same experimental conditions,the peak stress of Ti-6Al-4V-0.1B alloy was lower than that of Ti-6Al-4V matrix alloy,which was attributed to the refinement effect of trace B on Ti-6Al-4V matrix alloy.The peak strain of all samples appeared near 0.1,which was similar to Ti-6Al-4V alloy,indicating that the addition of a small amount of B did not affect the relationship between the peak stress and strain of the alloy.Perform linear regression on the true stress-true strain curve using the least square method,and then draw the lnσ-ln■and lnσ-1/T relationship curve（σwas the flow stress;■was the strain rate;T was the working temperature,K）.The stress exponent and activation energy of Ti-6Al-4V-0.1B alloy were calculated by using the lnσ-ln■and lnσ-1/T relationship curves to be n=6.67 and Q=926 k J·mol^-1,respectively （n was the stress exponent,Q was the apparent activation energy）.Compared with the matrix alloy,Ti-6Al-4V-0.1B alloy had a higher stress ex-ponent and strain activation energy.This was due to Ti B distributed at the grain boundary increasing the resistance to atomic diffusion and slowing down the dynamic softening process of thermal deformation.The microstructure of the alloy was characterized by optical microscope （OM）,scanning electron microscope （SEM） and electron backscatter diffraction （EBSD）.The experimental results showed that the microstructure of Ti-6Al-4V-0.1B alloy was obviously uneven after hot compression.The specific performance was that the surface area close to the anvil retains the as-cast structure,while the core area was fibrous structure with severe plastic deforma-tion.In the severe plastic deformation zone,the primary α phase was obviously bent and elongated,and tended to be aligned in the same direction.During the thermal compression process,when the temperature was higher （>900℃），more significant globulariza-tion occured,which was manifested by the appearance of more small equiaxed α phase between the elongated α phases.The globular-ization process was not only affected by the deformation temperature,but also by the strain rate.As the strain rate decreased,the de-gree of globularization of the α phase increased.The reason for the influence of strain rate on phase size was that the longer deformation time at low strain rate made the globularization process of α phase more fully performed,while the globularization process of α phase was insufficient at high strain rate.The true strain 0.9 during hot compression could not make the alloy complete the globularization process.Therefore,the room temperature structure of the alloy showed a mixed morphology composed of equiaxial α phase and primary α/β colony.During thermal compression,Ti B deflected under the action of compressive stress and tended to align parallel to the direc-tion of matrix fiber organization.When compressed at a low strain rate,due to the long plastic deformation time of the matrix,Ti B and the alloy matrix maintained good strain coordination,and there was no separation between the two.When deforming at a high strain rate,the strain mismatch between Ti B and the matrix caused Ti B to break and debond.The unfilled space after fracture and debonding was enlarged and displayed during metallographic corrosion,and the metallograph showed that there are obvious cavities at the end of Ti B.The existence of these cavities split the continuity of the matrix,leading to stress concentration and the formation and propagation of cracks.In the compressed sample,due to the formation of the feature that Ti B was arranged along the direction of the fibrous struc-ture,the discontinuous arrangement of Ti B in the matrix not only served as the origin of cracks,but also served as a channel for crack propagation.Therefore,the hot working process of Ti-6Al-4V-0.1B alloy should be carried out at a low strain rate.更多还原