Ti基非晶复合材料的强韧化机理研究

采用水冷铜坩埚磁悬浮熔炼-铜模吸铸法在真空及高纯氩气保护条件下制备了直径3mm的(Ti_0.5Ni_0.48M_0.02)₈₀Cu₂₀ (M=Fe、Ce、Zr)合金,研究了Fe、Ce、Zr对合金凝固组织中形状记忆晶相析出的变化规律,分析了该合金的室温力学行为与强韧化机理。研究发现,(Ti_0.5Ni_0.48M_0.02)₈₀Cu₂₀ (M=Fe、Ce、Zr)合金铸态结构均为非晶+形状记忆晶相(B2过冷奥氏体和B19_’热致马氏体)的复合结构,其中M=Fe的合金B2相体积分数析出最多,M=Zr的合金B19_,相体积分数最多。在室温压缩过程中,合金均表现出良好的综合力学性能,其中以M=Ce 的合金性能最优,断裂强度,屈服强度,塑性应变分别达到2645Mpa,1150Mpa和12.2%。合金在受压应力断裂后,组织中奥氏体相体积分数减小,马氏体相体积分数增加,同时在屈服后均表现出强烈的加工硬化行为。加工硬化速率和瞬时加工硬化速率随真应变的变化分为三个阶段,合金内部在压应力的作用下B2向B19_,相转变是合金强韧化的主要动力。M=Fe的合金加工硬化速率、平均加工硬化指数、瞬时加工硬化指数最大,加工硬化能力最强,M=Ce的合金次之,M=Zr的合金最弱。     

Mg-Zn-Y-Nd-Zr合金的显微组织、织构、力学性能

对Mg-Zn-Y-Nd-Zr合金的显微组织和力学性能进行了研究。结果表明,Nd元素的加入部分取代了W相（Mg₃Zn₃Y₂）中的Y元素,形成了新的第二相Mg₃Zn₃(Y, Nd)₂。热挤压后观察到由细小的等轴再结晶晶粒和粗大的细长未再结晶晶粒组成的典型双峰结构。Nd元素的加入促进了热挤压过程中的动态再结晶,随着Nd含量的增加,动态再结晶率增加,挤压态合金的整体织构强度减弱。Nd的加入细化了晶粒并改善了合金的力学性能。添加0.5%（质量分数）Nd时,挤压态合金表现出高强度和高塑性的良好结合：屈服强度为362 MPa,极限抗拉伸强度为404 MPa,延伸率为10.2%。时效处理后合金的抗拉伸强度进一步提高,峰值时效极限抗拉伸强度可达421 MPa。合金的高强度主要归功于超细再结晶晶粒和析出强化。     

放电等离子烧结制备低密度AlTiCrNiCu高熵合金及其组织性能研究

采用机械合金化和放电等离子烧结工艺制备了低密度AlTiCrNiCu高熵合金材料,重点研究了球磨时间对各元素粉末的合金化过程及烧结温度(950 ~ 1050 ℃)对高熵合金组织及力学性能的影响。结果表明：高熵合金粉末为单相BCC结构,随着球磨时间的增加,粉末粒径先变大后变小,其最终平均粒径大约为20 μm。高熵合金块体材料的相结构为BCC1(基体相)+BCC2(富Cr相)+FCC(富Cu相),密度为6.22 ~ 6.30 g/cm_³。烧结温度的升高,有利于高熵合金粉末的冶金结合,促进了高熵合金块材料的致密化。当烧结温度为1050 ℃时,AlTiCrNiCu高熵合金具有良好的综合力学性能,其屈服强度、压缩强度、塑性和显微硬度分别为1410 MPa,2000 MPa,9.13%和524 HV。分析认为高的烧结温度为各元素原子间的充分扩散提供了足够的能量。然而,TEM分析表明,高的烧结温度也促进了弥散的FCC富Cu相在晶界的聚集长大。     

机械合金化和真空热压烧结FeCoCrNiMn高熵合金的显微组织和力学性能（英文）

采用机械合金化和热压烧结制备FeCoCrNiMn高熵合金。结果表明,采用机械合金化得到纳米晶合金粉末,粉末相结构由面心立方结构(FCC)相以及少量的体心立方结构(BCC)相和非晶相组成。热压烧结后,合金中BCC相基本消失,同时伴随着σ相和M23C6相的析出;烧结温度的升高导致析出相颗粒明显长大。随着热压烧结温度从700℃升高到1000℃,合金塑性应变从4.4%增加到38.2%,而屈服强度从1682 MPa下降到774 MPa。经800℃和900℃烧结1 h的FeCoCrNiMn高熵合金具有较好的综合力学性能。     

中温轧制对新型镍基高温合金微观组织和高温力学性能的影响

本文采用EBSD、SEM、TEM和准静态高温拉伸试验研究了中温轧制变形量对新型镍基高温合金微观组织和高温(760 ℃)力学性能的影响。结果表明,中温轧制变形量对合金高温力学性能影响显著,相比于标准热处理(固溶处理+双级时效)合金试样的高温力学性能(σ_y=860 MPa,σ_uts=973 MPa和ε_f=3.5%),当中温轧制变形量为10%时,合金的σ_y提高了230 MPa,σ_uts提高了166 MPa,ε_f变化不明显,为4.1%；而当中温轧制变形量为80%时,合金的σ_y提高了190 MPa,σ_uts提高了165 MPa,ε_f大幅度增加,为22.5%,实现了合金高温强塑性匹配。760 ℃时合金强度和延伸率的提升是由于变形机制发生改变,随着变形量的增加,合金的主要变形机制由层错剪切向微孪生转变,微孪晶的形成既保证了合金的高温强度,又有利于延伸率的提高。     

“γ′相+孪晶”复合结构对高温合金强度及塑性的影响

本文通过调控低合金化、低层错能的Ni-Cr-Co基变形高温合金的“γ′相+孪晶”复合结构,分析了孪晶界对晶粒细化和强度提高的贡献以及复合结构对合金强塑性的影响。结果表明,合金在1090 ℃保温1 h的固溶处理后,锻态组织中粗大块状γ′相基本溶解,且此时组织中的孪晶含量高达51.65%。固溶态合金伸长率(42.9%)相比于锻态(26.8%)提升了63.6%,屈服强度为693 MPa(相比于锻态仅下降了3%),其中σ _tb=66.98 MPa,其贡献度基本和细晶强化的程度(77.4 MPa)持平。将固溶态合金经700 ℃/8 h/AC处理后的时效态合金孪晶含量为34.41%,同时组织引入大量沉淀强化相γ′相,构成“γ′相+孪晶”复合结构,此时时效态合金硬度、抗拉强度、屈服强度与伸长率(405 Hv,1042 MPa,864 MPa,49.76%)相较于固溶态(324.4 Hv,879 MPa,693 MPa ,42.9%,)均得到进一步提高,其中σ _tb=107.94 MPa。低合金化、低层错能的高温合金中的“γ′相+孪晶”复合结构实现了一定的强塑性匹配。     

放电等离子烧结WMoNbTaV-Al2O3 高熵合金组织及磨损性能

以金属粉末为原料,采用放电等离子烧结技术制备新型含α-Al₂O₃的WMoNbTaV难熔高熵合金,研究了烧结温度对合金致密化行为、相结构、显微组织和耐磨性能的影响。结果表明：在1800~1900 ℃烧结时,WMoNbTaV-Al₂O₃高熵合金基体具有单一bcc相结构,Al₂O₃的平均晶粒尺寸为1.15 μm。随着烧结温度升高,合金的晶粒尺寸增大,致密度和显微硬度也在不断增高,在1900 ℃烧结时硬度达到7967.4 MPa。1900 ℃烧结得到的合金具有优异的耐磨性,磨损量仅为1800 ℃烧结合金的一半。且WMoNbTaV-Al₂O₃高熵合金的耐磨性远高于纯W材料。当磨料粒度为37.5 μm时,1900 ℃烧结的合金磨损量为0.9 mg,磨损性能是纯W材料的83倍。     

TiZrHfNbSc难熔高熵合金组织和力学性能研究

利用真空电弧熔炼设备制备了新型TiZrHfNbSc难熔高熵合金,利用XRD、SEM、DSC等方法分析了合金的显微组织,利用显微硬度计、微控电子万能试验机测定了合金的硬度及力学性能。研究结果表明：TiZrHfNbSc难熔高熵合金为单一无序的BCC固溶体结构,晶格常数a=3.443?,合金密度约为7.16g/cm_³;合金的维氏显微硬度约380,屈服强度σ_0.2=650MPa,压缩变形率达到60%以上,合金的强化机制为固溶强化。     

Zn添加对Mg-8Al-2Sn镁合金组织和性能的影响

本文以Mg-8Al-2Sn变形镁合金为研究背景,通过在Mg-8Al-2Sn合金中添加0-2 wt.%含量的Zn元素,研究了Zn添加对Mg-8Al-2Sn挤压镁合金显微组织和性能的影响。研究结果表明,铸态Mg-8Al-2Sn-xZn合金的相组成主要是α-Mg相、Mg₁₇Al₁₂相和Mg₂Sn相。在添加Zn元素以后,合金中的共晶化合物的形态发生变化,由共晶组织变为离异共晶组织。挤压过后,晶粒组织尺寸更均匀。Zn元素的加入,会促进合金中第二相在挤压过程中的动态析出以及第二相尺寸的粗化。合金在时效中产生的析出相的数量也随着Zn含量的增多而增加。随着Zn含量的增加,挤压态和时效态合金的屈服强度和抗拉强度都随之增加。当Zn含量达到2 wt.%时,合金力学性能最好,其时效态的抗拉强度,屈服强度和延伸率分别是385 MPa, 291 MPa和6.44%。     

Mg-6Zn-1Mn-2Sn-0.5Ca合金挤压态和热处理态的组织与力学性能

利用光学显微镜、X 射线衍射仪、扫描电镜、透射电镜、硬度以及力学性能测试等对挤压态和时效处理的Mg?6Zn?1Mn?2Sn?0.5Ca 镁合金的显微组织和力学性能进行研究。研究结果表明：合金铸态的相组成为α-Mg, Mn, Mg7Zn3, Ca₂Mg₆Zn₃ 和CaMgSn相组成。挤压态组织为完全动态再结晶组织,晶粒尺寸约为2.8 μm。固溶时效处理(T6,180 ℃+10 h)后,合金的强度明显增加,屈服和抗拉分别为320 MPa 和390 MPa。合金强度的提高主要是由于晶界强化,固溶强化和析出强化作用。     

Microstructures and mechanical properties of TiAl alloy prepared by spark plasma sintering

A fine-grained TiAl alloy with a composition of Ti-47%Al(mole fraction) was prepared by double mechanical milling(DMM) and spark plasma sintering(SPS). The relationship among sintering temperature, microstructure and mechanical properties of Ti-47%Al alloy was studied by X-ray diffractometry(XRD), scanning electron microscopy(SEM) and mechanical testing. The results show that the morphology of double mechanical milling powder is regular with size of 20?40 μm. The main phase TiAl and few phases Ti₃Al and Ti₂Al were observed in the SPS bulk samples. For samples sintered at 1000 °C, the equiaxed crystal grain was achieved with size of 100?250 nm. The samples exhibited compressive and bending properties at room temperature with compressive strength of 2013 MPa, compression ratio of 4.6% and bending strength of 896 MPa. For samples sintered at 1100 °C, the size of equiaxed crystal grain was obviously increased. The SPS bulk samples exhibited uniform microstructures, with equiaxed TiAl phase and lamellar Ti₃Al phase were observed. The samples exhibited compressive and bending properties at room temperature with compressive strength of 1990 MPa, compression ratio of 6.0% and bending strength of 705 MPa. The micro-hardness of the SPS bulk samples sintered at 1000 °C is obviously higher than that of the samples sintered at 1100 °C. The compression fracture mode of the SPS TiAl alloy samples is intergranular fracture and the bending fracture mode of the SPS TiAl alloy samples is intergranular rupture and cleavage fracture.     

Microstructure,Mechanical and Corrosion Properties of AlCoCrFeNi High-Entropy Alloy Prepared by Spark Plasma Sintering

AlCoCrFeNi is one of the most widely studied alloy systems in the high-entropy alloy(HEA) area due to the interesting microstructure and mechanical properties.In this study,the AlCoCrFeNi alloy was prepared using spark plasma sintering(SPS) with pre-alloy powders obtained through gas atomization.Then,the sintered samples were annealed at 700,800 and900℃,and the effect of annealing temperature on the microstructure,mechanical and corrosion properties was studied.The results show that phase formation takes place during annealing process with the new phase(σ) and some nano scale BCC precipitates formation.The size and quantity of the nanoscale precipitates increase with increasing annealing temperature.The twin is also observed after annealing at 900℃.The annealing temperature has an obvious effect on the mechanical properties and corrosion resistance of the spark plasma sintered AlCoCrFeNi HEA.When the annealing temperature is 700℃,the hardness,yield strength and fracture strength reach the maximum with the value of 545 HV,1430 MPa and 2230 MPa,respectively.The compressive ratio reaches the maximum of 17.2%,with the annealing temperature increasing to 800℃.The corrosion resistance of the samples decreases with increasing the annealing temperature.     

Microstructure characteristics and mechanical properties of NbMoTiVWSix refractory high-entropy alloys

Refractory high-entropy alloys are considered as potential structural materials for elevated temperature applications. To obtain refractory high-entropy alloys with high strength, different amounts of Si were added into the NbMoTiVW refractory high-entropy alloys. The effects of Si on the phase constitution, microstructure characteristics and mechanical properties of NbMoTiVWSi_x alloys were investigated. Results show that when the addition of Si is 0, 0.025 and 0.05 (molar ratio), the alloys are consisted of primary BCC and secondary BCC in the intergranular area. When the addition of Si is increased to 0.075 and 0.1, eutectic structure including silicide phase and secondary BCC phase is formed. The primary BCC phase shows dendritic morphology, and is refined by adding Si. The volume fraction of intergranular area is increased from 12.22% to 18.13% when the addition of Si increases from 0 to 0.1. The ultimate compressive strength of the NbMoTiVW alloy is improved from 2,242 MPa to 2,532 MPa. Its yield strength is also improved by the addition of Si, and the yield strength of NbMoTiVWSi_0.1 reaches maximum of 2,298 MPa. However, the fracture strain of the alloy is decreased from 15.31% to 12.02%. The fracture mechanism of the alloys is changed from mixed fracture of ductile and quasi-cleavage to cleavage fracture with increasing of Si. The strengthening of alloys is attributed to the refinement of primary BCC phase, volume fraction increment of secondary BCC phase, and formation of eutectic structure by addition of Si.

     

粉末冶金FeCoNiCu0.4Al0.4高熵合金的热处理组织与性能

采用机械合金化(MA)与放电等离子烧结(SPS)相结合的方法制备出FeCoNiCu0.4Al0.4高熵合金,研究不同热处理温度对合金显微组织与力学性能的影响规律。结果表明:机械合金化后,FeCoNiCu0.4Al0.4高熵合金形成了单相的FCC固溶体,经1100℃SPS烧结后的块体组织仍为单相FCC结构,其压缩屈服强度、塑性应变和显微硬度分别为1165.1 MPa、45.2%和356.9 HV。经过热处理后,合金组织中生成了新的BCC相,且BCC相的含量随热处理温度的升高先增多后减少,500、600和700℃热处理后BCC相的含量分别为7%、30%和21%(体积分数)。退火态FeCoNiCu0.4Al0.4高熵合金的屈服强度随热处理温度的升高先升高后降低。当BCC相含量增多时,材料的屈服强度和硬度相应地提高,而塑性却显著降低。     

Fabrication,microstructure and mechanical property of a novel Nb-rich refractory high-entropy alloy strengthened by in-situ formation of dispersoids

We fabricated Nb₄₂Mo₂₀Ti₁₃Cr₁₂V₁₂Ta₁, a novel refractory high-entropy alloy (RHEA) enriched with niobium (Nb), by following a high-energy ball milling and spark plasma sintering (SPS) method. The microstructure of the bulk RHEA formed a single body-centered cubic (BCC) matrix with in-situ-formed carbide dispersoids. The combination of the effect of the severe deformations caused by the milling, the short sintering time, and the impedance of the grain growth caused by the dispersoids led to the formation of nano-sized grains, in spite of the high sintering temperature of 1200 °C. This resulted in outstanding mechanical properties. The bulk Nb₄₂Mo₂₀Ti₁₃Cr₁₂V₁₂Ta₁ RHEA exhibits a compressive yield strength of 2680 MPa, a maximum strength of 3896 MPa, and a Vickers hardness of 741 HV. The excellent mechanical properties of the alloy can be attributed to the strengthening of the dispersion and the solid solution, coupled with the grain refinement effects.     

CrFeCoNiB0.05Tix高熵合金的显微组织和力学性能

采用机械合金化和放电等离子烧结工艺制备了CrFeCoNiB_0.05Ti_x(x=0.2、0.4、0.6、0.8、1.0)高熵合金材料,通过X射线衍射分析、扫描电镜观察和能谱分析以及维氏硬度测试和压缩强度测试等,研究了Ti含量对高熵合金微观组织和力学性能的影响。结果表明,CrFeCoNiB_0.05Ti_x(x=0.2、0.4、0.6、0.8、1.0)高熵合金由FCC、BCC和α相组成。当x=1.0时,合金由BCC结构转向HCP结构并析出新相Laves相,其具有最高硬度416.54 HV0.2。当x=0.8时,合金达到最大抗压强度586.3 MPa。     

Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process.     

Effect of nitrogen on microstructure and mechanical properties of CrMnFeVTi6 high entropy alloy

In order to evaluate interstitial strengthening effect on the properties of high entropy alloy (HEA), a nitrogen-doped CrMnFeVTi6 HEA was fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). XRD, SEM, TEM and FIB were used to characterize the phase composition and microstructure of this material. The sintered bulk HEA exhibits a microstructure comprising TiN_x, BCC, Laves and B2 phases. The HEA exhibits high yield strength (>2729 MPa) and hardness in lower temperature range of <380 °C. Quantitative calculations of the contributions from each strengthening mechanism in the BCC phase indicate that the interstitial strengthening by nitrogen is the dominant mechanism. Nitrogen additions in the BCC phase can produce a yield strength increase of ∼634 MPa/at.%, which is much higher than the strengthening effects of carbon or boron additions in other alloys. This demonstrates that adding nitrogen is a viable approach for enhancing the strength of HEAs.     

烧结方式对CoCrNi中熵合金组织及力学性能的影响

采用机械合金化法（MA）球磨制备CoCrNi中熵合金原料粉末,结合放电等离子烧结（SPS）或高真空烧结制取CoCrNi中熵合金,研究了球磨时间以及退火对CoCrNi中熵合金原料粉末微观形貌、颗粒尺寸及相结构的影响规律,对不同烧结方式制备的合金块体进行微观结构及力学性能研究。结果表明：随着球磨时间的延长,各单质粉末颗粒尺寸不断减小并逐渐融合,在球磨25 h后,原料粉末主要为fcc固溶体结构,还有少量的bcc相;在后续烧结过程中,少量bcc相发生相转变,组织中只有fcc相结构;退火烧结样品的弹性模量为6.57 GPa,是真空烧结的1.55倍,屈服强度为279.28 MPa,与真空烧结后样品的屈服强度相当,退火烧结的延伸率为35.97%,明显大于直接真空烧结;SPS烧结的块体合金表现出高达793.72MPa的屈服强度和61.08%的塑性应变,且维氏硬度(HV)达到3910.2MPa,与其它2种烧结方法相比,SPS在实现高熵合金（HEAs）快速低温烧结方面更具潜力。     

YbB6 对Ti-6Al-4V钛合金组织和性能的影响

采用放电等离子烧结（SPS）制备了含YbB₆的Ti-6Al-4V钛合金,并研究了YbB₆对Ti-6Al-4V钛合金显微组织和力学性能的影响。结果表明,随着YbB₆含量的增加,复合材料的显微组织发生转变,晶粒明显细化,原位反应生成的TiB晶须和Yb₂O₃颗粒有利于复合材料力学性能的提高。此外,当添加0.6%（质量分数）YbB₆后,烧结样品的相对密度、显微硬度、屈服强度、极限拉伸强度和延伸率分别为99.43%、4030 MPa、903 MPa、1148 MPa和3.3%。与Ti-6Al-4V试样相比,其数值分别提高了0.37%、13.8%、38.07%和17.14%。强化机制主要是组织转变、晶粒细化和弥散强化。随着YbB₆含量的增加,断裂方式主要为韧性断裂和脆性断裂。