硅化物涂层对Nb?Ti?Al合金力学性能的影响

采用真空电弧炉熔炼法制备低密度Nb?Ti?Al合金铸锭,利用料浆烧结法在铸锭表面涂覆Si?Cr?Ti复合硅化物涂层,使用万能电子拉伸试验机对合金试样和涂层试样进行力学性能测试,研究硅化物涂层对试样力学性能的影响。结果表明,与合金试样相比,涂覆涂层后的低密度铌合金室温力学性能（抗拉强度、屈服强度及延伸率）显著下降。为进一步研究涂覆涂层合金力学性能下降的原因,采用扫描电子显微镜和能谱仪对合金试样和涂层试样进行显微组织观察、涂层/基体界面成分分析及C含量（质量分数）测定。结果表明,涂层试样力学性能下降的主要原因包括涂覆涂层后合金晶粒显著长大,合金中强化元素Al的向外扩散,脆性相Nb₃Al的形成以及Si?Cr?Ti涂层对合金产生的“渗沉效应”。     

陶瓷颗粒增强扩散合金化钢复合材料的微观结构和力学性能

采用传统粉末冶金工艺制备了陶瓷颗粒增强Fe?0.5Mo?1.75Ni?1.5Cu?0.7C扩散合金化钢复合材料,选用的陶瓷颗粒为SiC、TiC和TiB₂。采用光学显微镜和扫描电子显微镜观察了烧结材料微观结构,并对烧结材料的硬度、强度和摩擦磨损性能进行了测试。结果表明,由于SiC和TiB₂与基体的化学相容性好,陶瓷颗粒与基体界面结合良好;由于TiC颗粒具有极高的化学稳定性,TiC颗粒与基体界面结合情况不理想。随着陶瓷相含量（质量分数）的增加,添加SiC和TiC的烧结试样相对密度降低;添加TiB₂的烧结试样相对密度先增加后降低,当添加TiB₂质量分数为0.9%时达到最大值。随着陶瓷含量增加,添加SiC和TiB₂烧结试样的硬度增大,当陶瓷相质量分数超过1.2%时,硬度增加缓慢;添加TiC烧结试样的硬度先增加后降低,当添加TiC质量分数为0.9%时达到最大值。随着陶瓷相含量增加,添加SiC和TiC烧结试样的强度降低,少量添加SiC对强度没有明显损害;添加TiB₂烧结试样的强度先增加后降低,当添加TiB₂质量分数为0.6%时达到最大值（971.7MPa）,比基体提高了14.1%以上。添加陶瓷相对烧结钢性能的积极影响依次是TiB₂、SiC和TiC。     

烧结温度与混粉比例对双尺度钛合金组织与性能的影响

采用高能球磨-放电等离子烧结技术制备具有双尺度显微组织的Ti-6Al-4V合金,并研究烧结温度和加入未球磨粉末的比例对烧结试样显微组织及力学性能的影响。实验结果表明:当球磨时间为6 h时,由于球磨粉末内部的应变量不均匀,球磨粉末烧结试样的显微组织均由粗晶网篮组织和细晶等轴组织组成。随烧结温度升高,烧结试样的密度逐渐提高,细晶区的晶粒尺寸逐渐增大,材料强度呈先上升后下降的趋势。在球磨粉末中加入一定比例的未球磨粉末可显著提高烧结材料的塑性,并且保持较高的强度。当球磨粉末与未球磨粉末按质量比4:1混合、SPS烧结温度为850℃、保温时间为4min时,烧结材料相对密度达到99.0%,细晶区晶粒尺寸为1~2μm,烧结试样获得最佳强度-塑性组合,其拉伸屈服强度为1012 MPa,断裂强度为1056 MPa,伸长率为10%。     

烧结温度对内燃机用TiZrVMo高熔合金组织和力学性能的影响

运用放电等离子烧结方法(SPS)制备TiZrVMo合金,并通过控制不同的烧结温度获得了不同力学特性与组织结构的试样。测试结果表明,对合金烧结处理后其基体中形成了包含BCC与FCC两种晶体结构,BCC组织形成了比FCC组织更高的衍射峰。当烧结温度增加后,晶粒尺寸呈现增大的现象,塑性先增大后降低。经过1100℃烧结得到的试样压缩屈服强度为1501.4MPa,塑性应变31.4%。随着烧结温度的增加,屈服强度先减少后增加,塑性应变先增大后减小。当烧结温度上升后,合金材料从准脆性断裂逐渐转变为微孔聚集型断裂,之后形成了大尺寸晶粒并发生沿晶断裂的现象,呈现脆性解理断裂的特点。     

添加纳米Ti(C,N)对粗晶WC-8Co硬质合金微观组织和力学性能的影响

将粒度为0.2μm的Ti(C,N)纳米粉末添加到粗晶WC-8Co硬质合金中，采用低压烧结技术制备了WC-xTi(C,N)-8Co系列硬质合金。利用XRD、SEM和EDS研究了添加纳米Ti(C,N)的硬质合金试样的物相组成和微观组织，并分析和讨论了合金的钴磁、矫顽磁力、洛氏硬度和抗弯强度等性能。结果表明，添加纳米Ti(C,N)烧结后的合金均出现了典型的Ti(C,N)芯-环结构，提高了硬质合金的硬度。然而，微量的Ti(C,N)添加会导致合金的力学性能下降，当添加量达到5%时，合金的综合力学性能最好，但当添加量达到15%以上时，基体出现脱碳相，导致合金的抗弯强度大幅下降。     

稀土对HAl62-3-3-0.7合金组织和性能的影响

通过对合金成分的调整分别配制了添加不同量稀土元素的试验用HAl62-3-3-0．7合金。借助金相与扫描电镜观察和分析了各合金的显微组织结构,运用模拟设备测试了各合金的力学性能。文章阐述了稀土元素对该类高强度耐磨黄铜的组织和性能的影响,试验表明适量加入稀土会显著细化晶粒,过量的稀土会导致在合金显微组织中形成线形富稀土相。随着合金中稀土含量的增加,合金的硬度升高,但当稀土含量超过0．1％时,由于线形富稀土相的形成,反而会使合金的力学性能下降。     

碳化硅纳米线增强钛基复合材料的制备与性能研究

采用球磨法将Ti60合金粉末与碳化硅纳米线(SiCnw)混合,通过放电等离子活化烧结工艺制备SiCnw/Ti60复合材料.利用扫描电子显微镜、X射线衍射仪和万能力学试验机研究复合材料的组织形貌、物相结构和力学性能.结果表明,在Ti60合金中添加SiCnw后,基体晶粒尺寸显著减小,当SiCnw添加量为0.1％(质量分数)...     

固溶温度对7050铝合金组织及性能的影响

采用光学显微镜(OM)、扫描电子显微镜(SEM)、力学性能测试及断裂韧性试验研究了固溶温度对7050铝合金组织和力学性能的影响。结果表明,随着固溶温度的升高,合金晶粒发生再结晶的比例逐渐增大,合金中粗大第二相粒子逐渐减少而后趋于稳定。另外,随着固溶温度升高,合金的强度以及断裂韧性先升高后降低,试样断裂时穿晶断裂的比例逐渐增大,穿晶韧窝更多、更深,韧窝中的粗大第二相明显减少。当固溶温度超过480℃后,合金断裂方式主要为沿晶断裂。     

发动机用石墨烯增强TC11合金放电等离子烧结制备参数优化及力学性能研究

通过添加石墨烯提高了放电等离子烧结（spark plasma sintering, SPS）制备发动机用耐高温TC11合金的力学性能,研究了不同烧结参数下TC11合金的密度,并观察了合金显微组织,分析了合金力学性能的影响因素。研究结果表明:随着烧结温度增加,试样密度先增加后平稳;提高烧结压力后,试样密度发生了略微上升。随着烧结温度的上升,更多α相转变成了高温β相,形成了相对稳定的β相比例。随着烧结时间的增加,合金室温压缩强度表现为升高的趋势。提高烧结压力后,TC11合金获得了更高的室温与高温力学强度。通过实验最终确定烧结时间5 min、温度900 ℃与压力50 MPa时制备的TC11合金具有最优力学性能。     

Y_2O_3和Ti含量对弥散强化铁合金组织结构和性能的影响

以水热法制备的不同Y_2O_3含量的弥散强化(ODS)铁合金粉末为原料,通过机械合金化工艺加入质量分数分别为0、0.8%、2%的合金元素Ti,再采用放电等离子烧结(SPS)工艺制备弥散强化铁合金。采用扫描电镜(SEM)和电子拉伸试验机对样品进行观察和检测,研究弥散相Y_2O_3和合金元素Ti含量对弥散强化铁的微观组织和力学性能的影响。结果表明:当不加入合金元素Ti而Y_2O_3弥散相含量(质量分数)为1.0%时,弥散强化铁达到最佳力学性能,抗拉强度537 MPa;加入0.8%的合金元素Ti后,弥散相颗粒明显细化,抗拉强度和硬度均明显提高,抗拉强度达到710 MPa。     

Sintering behaviour and mechanical characterisation of Ti64/xTiN composites and bilayer components

Ceramic particle reinforcement can be used to improve the surface properties of Ti6Al4V (Ti64) alloy. Powder metallurgy route is a promising method to fabricate such reinforced Ti64 components. To assess the relevance of this technique, this work investigates the effect generated by the addition of TiN particles in Ti64 powder during free sintering. TiN reinforcement particles were randomly distributed in the Ti64 matrix with three different concentrations in two configurations: completely reinforced and unreinforced–reinforced bilayer. Dilatometry was used to obtain the shrinkage kinetics of samples at 1200, 1300 and 1400°C under inert atmosphere and to investigate the impact of reinforced particles on the sintering behaviour. The microstructure of sintered materials was shown to be lamellar in the unreinforced material and equiaxed in reinforced materials. Finally, the Vickers microhardness measurement showed the huge benefit of adding TiN particles to increase the mechanical strength of the Ti64 alloy.     

稀土元素Y对粉末冶金2A12铝合金组织和力学性能的影响

在铝合金粉末中添加质量分数为0、0.2%、0.4%及0.6%的稀土元素Y, 利用粉末冶金法制备2A12铝合金。通过金相组织观察、X射线衍射分析、扫描电子显微形貌表征、能谱分析及力学性能测试等手段, 研究了稀土元素Y对粉末冶金2A12铝合金组织和性能的影响, 总结了Y在铝合金中的分布特征。结果表明, 当稀土元素Y的质量分数为0.2%时, 2A12铝合金抗拉强度最高, 塑性最好; 添加Y可以抑制铝合金晶粒在烧结过程中的长大; 稀土元素Y主要以YAl相、Cu₂Y相和YAl₂相的形式分布在基体晶界处, 少量Y固溶在铝基体中。     

高强AZ61Mg?18%Ti复合材料的制备及力学性能

通过机械球磨、真空热压和热挤压制备了AZ61Mg?18%Ti（质量分数）复合材料,研究了复合材料的微观组织、室温力学性能和强化机制。结果表明,采用真空热压+热挤压制备的复合材料镁基体平均晶粒尺寸为180 nm,Ti颗粒及纳米级Ti₃Al相弥散分布于镁基体中,Ti颗粒和Ti₃Al相平均尺寸分别为265 nm和10 nm。超细晶AZ61Mg?18%Ti复合材料具有优异的室温力学性能,其屈服强度、抗压强度和断裂应变分别达到606 MPa、698 MPa和12%。     

烧结温度及Y2O3对9Cr-RAFM钢性能的影响

采用粉末冶金技术,以球磨-模压-真空烧结工艺制备2种9Cr-RAFM钢:以0.3%Y2O3(质量分数)为弥散相的ODS 9Cr铁基高温合金和不添加Y2O3的Non-ODS 9Cr铁基高温合金。研究烧结温度及Y2O3对RAFM钢的力学性能和微观组织的影响。研究结果表明:采用球磨-模压-真空烧结工艺制备的ODS合金的综合力学性能高于Non-ODS合金,并且在1 390℃烧结,保温2 h条件下制备的ODS合金具有最佳的综合力学性能(抗拉强度600 MPa,伸长率23.1%)。并对不同球磨时间的合金粉末进行XRD物相分析,用SEM及能谱分析技术研究Y2O3影响RAFM钢的微观组织成分和力学性能的机理。     

微合金化对电子封装用高硅铝合金微观组织与性能的影响

采用快速凝固-粉末冶金法制备电子封装用高硅铝合金（Al-50 %Si）,研究添加单质Cu粉对微观组织、力学性能和热物理性能的影响.采用扫描电子显微电镜（SEM）、X射线衍射仪（XRD）等手段,分析Cu含量（0~2 %）对微观组织和相组成的影响,并建立与力学性能和热物理性能之间的关系.结果表明:当Cu含量不高于1 %时,高硅铝合金微观组织中Si相尺寸和形貌改变不明显;拉伸强度和抗弯强度均随着Cu含量增加而迅速上升,并在2 %Cu时达到极大值268.4 MPa和422.6 MPa,相对于合金化前提高44.9 %和46.7 %;Cu含量对合金热膨胀系数（CTE）的影响不明显,但是基体中细小的Al₂Cu相不利于导热性能（热导率下降7.5 %）.综上,电子封装用高硅铝合金中添加1 %Cu时,可以在基本保持原有组织和热物理性能的情况下,提高强度20 %以上.      

Microstructural modification of as-cast Al-Si-Mg alloy by friction stir processing

Friction stir processing (FSP) has been applied to cast aluminum alloy A356 plates to enhance the mechanical properties through microstructural refinement and homogenization. The effect of tool geometry and FSP parameters on resultant microstructure and mechanical properties was investigated. The FSP broke up and dispersed the coarse acicular Si particles creating a uniform distribution of Si particles in the aluminum matrix with significant microstructural refinement. Further, FSP healed the casting porosity. These microstructural changes led to a significant improvement in both strength and ductility. Higher tool rotation rate was the most effective parameter to refine coarse Si particles, heal the casting porosity, and consequently increase strength. The effect of tool geometry was complicated and no systematic trend was observed. For a standard pin design, maximum strength was achieved at a tool rotation rate of 900 rpm and traverse speed of 203 mm/min. Post-FSP aging increased strength for materials processed at higher tool rotation rates of 700 to 1100 rpm, but exerted only a marginal effect on samples prepared at the lower rotation rate of 300 rpm. Two-pass FSP with 100 pct overlapping passes resulted in higher strength for both as-FSP and post-FSP aged conditions.     

Microstructure and mechanical properties of Mg-7Zn-3Al alloy with Nd and Y additions

The effects of combined addition of 0.6 wt.% Nd and 0.4 wt.% Y on the microstructure and mechanical properties of Mg-7Zn-3Al alloy were investigated.The results indicated that the Nd and Y addition led to obvious dendrite coarsening.However,it could modify the morphology and distribution of-Mg 32(Al,Zn) 49 intermetallics.Moreover,Al 2 REZn 2 phase could be introduced into the alloy with the Nd and Y addition.With the effective second-phase strengthening,the ultimate tensile strength and elongation in as-cast state can be improved by the Nd and Y addition.After ageing treatment,the alloy with the Nd and Y addition exhibited better precipitation strengthening effects by forming finer MgZn 2 and Mg 32(Al,Zn) 49 precipitates into the-Mg matrix.As a result,the yield and ultimate strength of Mg-7Zn3Al-0.6Nd-0.4Y alloy could be increased to 182 and 300 MPa by peak-ageing treatment.     

Processing and Mechanical Properties of Cast Al (Mg,Mn)-Al2O3 (MnO2) Composites Containing Nanoparticles and Larger Particles

The composites reinforced with nanoparticles result in improved strength and ductility while those containing coarser particles of micron size have limited ductility. The present study investigates the outcome of mechanical properties in a composite reinforced simultaneously with coarse and fine particles. High energy milling of manganese dioxide particles with excess of aluminum powder ensures that nanoparticles generated, either of MnO₂ or alumina, are mostly separate and surrounded by aluminum particles. The milled powder when added to aluminum alloy melt, the excess aluminum particles will melt leaving behind separate oxide nanoparticles without significant agglomeration. Different amounts of milled powder mix have been stirred into molten aluminum alloy where nanoparticles of MnO₂ react with melt to form alumina. The resulting slurry is cast into composites, which also contains coarser (nearly micron size) alumina particles formed by internal oxidation of the melt during processing. The microstructure of the composites shows good distribution of both the size categories of particles without significant clustering. The oxide particles are primarily γ-alumina in a matrix of aluminum-magnesium-manganese alloy containing some iron picked up from the stirrer. These composites fail during tensile test by ductile fracture due to debonding of coarser particles. The presence of nanoparticles along with coarser particles in a composite improves both strength and ductility considerably, presumably due to delay in debonding of coarser particles to higher stress because of reduced mismatch in extension caused by increased strain hardening in presence of nanoparticles in the matrix. The composites containing only coarser oxide particles show limited strength and ductility attributed to early debonding of particles at a relatively lower stress due to larger mismatch in extension between matrix and larger particles. Higher addition of powder mix beyond a limit, however, results in deterioration of mechanical properties, possibly due to clustering of nanoparticles. The present work, however, did not optimize the relative amounts of the different sized particles for achieving maximum ductility.     

Synthesis and characterisation of Ti6Al4V/xTa alloy processed by solid state sintering

ABSTRACT

This work investigates the effect of Ta particle addition into a Ti6Al4V alloy processed by solid state sintering. The volume fraction of Ta ranged between 0 and 30?vol.-%. The sintering kinetics of powder mixes are evaluated by dilatometry. Sintered materials are characterised by SEM and XRD, and their mechanical properties are obtained from microhardness and compression tests. Sintering behaviour and final microstructure are affected by Ta particles, which slow down the densification, lower the temperature of α-to-β phase transition and stabilise the β phase. Mechanical properties, as microhardness, Young’s modulus and yield stress, depend on the microstructure reached after sintering and on the residual porosity. An equation expressing the Young’s modulus of Ti6Al4V/xTa alloy as function of x and porosity is proposed and validated. The materials with at least 20?vol.-% of Ta exhibited a high strength to modulus ratio, which is suitable for orthopaedic implants.