旁路耦合等离子弧钛合金增材制造组织与性能的研究

利用旁路耦合等离子弧焊试验平台,对TC4钛合金进行等离子弧增材制造。观测堆垛样的组织及显微硬度,结合增材制造过程中所测的热循环曲线,分析旁路电流、堆垛顺序对TC4钛合金堆垛样组织和性能的影响。结果显示,在旁路耦合电弧焊TC4钛合金增材制造过程中,旁路电流的引入会使堆垛样组织的枝晶变粗、间距减小,对堆垛层产生较大深度的强化效果;显微硬度沿着堆积高度方向呈增大趋势;堆垛顺序使堆垛层的硬度有一定的提升,导致晶枝生长发生改变。

铣削激光增材制造TC4钛合金铣削力的研究

为满足工件的表面质量的要求,对激光增材制造的TC4钛合金进行铣削加工,从而可以实现更高精度的加工要求。为研究铣削用量对铣削激光增材制造钛合金的铣削力的影响,建立了铣削激光增材制造(selective laser melting, SLM) TC4钛合金的仿真模型;另外,采用与仿真模型相同的铣削用量进行了铣削试验,对仿真和试验结果进行了极差分析。分析结果表明,轴向切深a_(p)对铣削力影响程度最大、其次为铣削速度v_(c)和每齿进给量f_(z)。最优铣削参数为铣削速度v_(c)=55 m/min,每齿进给量f_(z)=0.04 mm/z,轴向切深a_(p)=0.3 mm。铣削仿真和试验的误差对比分析结果表明,所建立的铣削仿真模型是合理可行的,因此,基于此铣削仿真模型,采用单因素试验法进行了仿真和铣削试验,研究结果表明,随着铣削速度、轴向切深和每齿进给量的增大,铣削力增大,但当铣削速度超过75 m/min时铣削力反而减小。

增材制造TC4钛合金的动态力学行为研究

增材制造TC4钛合金是具有优良的力学性能和工艺性能的金属材料,在航空航天领域已得到重要应用.近年来,在塑性力学的研究中,探究应力状态对金属材料变形和失效行为的影响得到广泛关注,然而大部分的研究都是在准静态下完成的,对于中高应变率下金属材料变形失效的研究较少.本文从增材制造TC4钛合金的基本力学性能出发,考虑应力状态和应变率对其变形和失效行为的影响,采用应力三轴度η和罗德角参数■表征应力状态,设计了相应的试样形式和实验方法.利用电子万能实验机、高速液压伺服实验机以及分离式Hopkinson杆,结合数字图像相关法分析对材料在不同应变率、不同应力状态下的力学性能进行了测试,获得其变形和失效特性.为得到试样内部应力状态历程参数和应变场,通过ABAQUS进行数值仿真,得到试样应变最大处的应力状态历程参数和失效应变.以实验测试和仿真分析结果为基础,对传统MMC失效模型进行了修正,建立了全面考虑应变率、应力三轴度和罗德角效应的增材制造TC4材料的失效模型;同时建立了考虑应力三轴度η和应变率效应的Johnson-Cook失效模型.并通过对增材制造TC4钛合金平板进行高速冲击实验和数值仿真,验证了本文拟合的该材料的本构模型和失效模型描述高应变率下变形失效行为的有效性.

热处理对增材制造TC4钛合金组织结构及耐蚀性能的影响

增材制造TC4钛合金存在亚稳态相结构,其对合金的组织结构和耐蚀性有着明显的影响。基于此,对增材制造TC4钛合金进行了不同工艺的热处理,采用扫描电镜(SEM)、X射线衍射(XRD)、残余应力测量和电化学分析等研究了热处理对增材制造TC4钛合金组织结构、残余应力与耐蚀性能的影响。结果表明:热处理工艺对TC4钛合金的组织结构具有重要影响,当钛合金在940℃以上保温1 h后冷却,组织由亚稳态α′相转变为α+β相及少量次生α相,与炉冷相比,水冷条件下钛合金β相含量更高;当热处理温度为800、940和1080℃时,钛合金表面的残余应力值较低;钛合金的耐腐蚀性能与组织结构和残余应力有着密切关系,钛合金中α相晶粒越细小,β相含量越高,残余压应力值越大,其耐蚀性越好。当热处理温度为1020℃时,钛合金表面残余压应力值为470 MPa,耐蚀性能良好。

增材制造Ti-6Al-4V合金断裂行为与应力三轴度关系研究

研究应力三轴度与增材制造钛合金材料断裂行为的相关性,对分析增材制造钛合金的断裂失效过程有着重要的作用和意义。对光滑圆棒和缺口圆棒试件在准静态下进行单轴拉伸试验,结合数值仿真分析得到试件的应力三轴度分布和断裂应变,研究了增材制造钛合金在不同应力三轴度下的韧性断裂行为。通过扫描电子显微镜观察试件断口表面的形貌,分析不同应力三轴度下增材制造钛合金的断裂机理。研究发现,在中高应力三轴度范围内,增材制造钛合金的断裂应变随应力三轴度的升高而降低;缺口圆棒试件的起裂位置随缺口半径的减小从最小截面中心处逐渐转移至边缘处。

激光增材制造钛合金织构跨尺度分析

针对增材制造钛合金的组织特点,采用EBSD以及XRD的方法对增材制造TC11合金进行了织构分析,探讨TC11合金从微米级微观织构到厘米级宏观织构的变化规律,分析了EBSD扫描面积大小对织构分析结果的影响。结果表明,采用大面积EBSD拼接扫描的织构分析结果与XRD宏观分析结果一致。TC11合金β相具有<001>∥沉积方向的丝织构及弱(001)[010]板织构,α相的主织构为<160 16 19>∥[001]、<2110>∥[001]丝织构。

New development of powder metallurgy in automotive industry

The driving force for using powder metallurgy(PM)mostly relies on its near net-shape ability and cost-performance ratio.The automotive application is a main market of PM industry,requiring parts with competitive mechanical or functional performance in a mass production scale.As the automobile technology transforms from traditional internal combustion engine vehicles to new energy vehicles,PM technology is undergoing significant changes in manufacturing and materials development.This review outlines the challenges and opportunities generated by the changes in the automotive technology for PM.Low-cost,high-performance and light-weight are critical aspects for future PM materials development.Therefore,the studies on PM lean-alloyed steel,aluminum alloys,and titanium alloy materials were reviewed.In addition,PM soft magnetic composite applied to new energy vehicles was discussed.Then new opportunities for advanced processing,such as metal injection molding(MIM)and additive manufacturing(AM),in automotive industry were stated.In general,the change in automotive industry raises sufficient development space for PM.While,emerging technologies require more preeminent PM materials.Iron-based parts are still the main PM products due to their mechanical performance and low cost.MIM will occupy the growing market of highly flexible and complex parts.AM opens a door for fast prototyping,great flexibility and customizing at low cost,driving weight and assembling reduction.

Improved mechanical and wear properties of Ti-35Nb-5Ta-7Zr-xSi alloys fabricated by selective electron beam melting for biomedical application

As the next generation biomedical titanium alloy, β-type titanium alloys are excellent candidates for biomedical applications due to the relative low elastic modulus and the contained non-toxic elements. However, the relative low strength and unsatisfactory tribological property are undesired for load-bearing implant applications. In this study, 0-5 at% Si was added to the classic Ti-35Nb-5Ta-7Zr alloy to improve its strength and wear resistance, and the(Ti-35Nb-5Ta-7Zr)1-x-Six(x=0, 1 at% and 5 at%) alloy were fabricated by selective electron beam melting(SEBM)technology. The results indicated that Si addition significantly increases in compressive yield strength, which is mainly due to grain refinement strengthening. At the same time, the wear rate of the as-built TNTZ-5Si alloy in SBF solution was only ~30% of the Ti-6Al-4V alloy. Consequently, the TNTZ-5Si alloy showed an excellent combination of compressive yield strength, elastic modulus and wear resistance for potential load-bearing implant applications.

Influence of heat treatments on microstructure and mechanical properties of laser additive manufacturing Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy

The effect of heat treatments on laser additive manufacturing(LAM)Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy(TC17)was studied aiming to optimize its microstructure and mechanical properties.The as-deposited sample exhibits features of a mixed priorβgrain structure consisting of equiaxed and columnar grains,intragranular ultra-fineαlaths and numerous continuous grain boundaryα(αGB).After being pre-annealed inα+βregion(840°C)and standard solution and aging treated,the continuousαGB becomes coarser and the precipitate free zone(PFZ)nearby theαGB transforms into a zone filled with ultra-fine secondaryα(αS)but no primaryα(αP).When pre-annealed in singleβregion(910°C),allαphases transform intoβphase and the alloying elements distribute uniformly near the grain boundary.DiscontinuousαGB and uniform mixture ofαP andαS near grain boundary form after subsequent solution and aging treatment.The two heat treatments can improve the tensile mechanical properties of LAM TC17to satisfy the aviation standard for TC17.

Effect of deposition rate on microstructure and mechanical properties of wire arc additive manufacturing of Ti-6Al-4V components

Wire arc additive manufacturing(WAAM)is a novel manufacturing technique by which high strength metal components can be fabricated layer by layer using an electric arc as the heat source and metal wire as feedstock,and offers the potential to produce large dimensional structures at much higher build rate and minimum waste of raw material.In the present work,a cold metal transfer(CMT)based additive manufacturing was carried out and the effect of deposition rate on the microstructure and mechanical properties of WAAM Ti-6Al-4V components was investigated.The microstructure of WAAM components showed similar microstructural morphology in all deposition conditions.When the deposition rate increased from 1.63 to 2.23 kg/h,the ultimate tensile strength(UTS)decreased from 984.6 MPa to 899.2 MPa and the micro-hardness showed a scattered but clear decline trend.

Effect of Nd addition on microstructure and tensile properties of laser additive manufactured TC11 titanium alloy

Single-layer and multilayer laser additive manufacturing(LAM)for TC11 alloy with different Nd additions was conducted and the effect of Nd addition on microstructure and properties was studied.With the addition of Nd,the aspect ratio of melting pools of single-layer specimens increases and the columnar-to-equiaxed transition occurs.The originalβgrain size andαplate width of TC11−1.0Nd are significantly reduced compared with those of pure TC11 specimens.It is proposed that the evenly distributed fine Nd_(2)O_(3) precipitates of about 1.51μm are formed preferentially during rapid solidification of melting pool,and they serve as heterogeneous nucleation particles to refine the microstructure in the subsequent solidification and solid-state phase transformation.Due to the multiple effects of Nd on the microstructure,the ultimate tensile strength of TC11−1.0Nd increases,while the yield strength,ductility and microhardness decrease compared with those of pure TC11.

选区激光熔化TC4小裂纹扩展特性数值模拟

发展了一种考虑微观组织的选区激光熔化(SLM)钛合金TC4小裂纹扩展数值模拟方法。基于SLM TC4的微观组织观测结果,利用Voronoi算法并通过晶体取向筛选,实现了微观组织建模。在此基础上,采用扩展有限元法建立了SLM TC4材料小裂纹扩展行为模拟方法,探究沉积方向以及晶粒尺寸、晶体取向等微观组织对小裂纹扩展速率的影响规律。结果表明:沉积方向影响材料的裂纹扩展抗力,沉积方向与裂纹扩展方向平行时,材料抵抗疲劳小裂纹扩展的性能相对更好。晶粒尺寸影响小裂纹扩展速率,晶粒尺寸越大,小裂纹扩展速率越快。晶体取向影响速率的波动性,不同晶体取向材料的小裂纹扩展速率上下界有明显差异。