AlxMo0.5Nb0.5Ta0.5Ti1.5难熔高熵合金组织和性能研究

研究了Al_xMo_0.5Nb_0.5Ta_0.5Ti_1.5难熔高熵合金的微观组织结构和力学性能，从Al元素在该体系合金中固溶强化作用以及Al和过渡族元素的强键合作用两方面对合金性能变化进行了分析。结果表明，Al含量在0～0.75范围内，合金均呈BCC结构类型，随Al含量增加，合金的树枝状凝固组织逐渐细化，硬度增加。在室温条件下，低Al含量(x≤0.3)合金在压缩应变达70%不发生断裂，高Al含量(x≥0.4)合金则表现出明显脆性。在高温条件下，随Al含量增加，合金体系理论熔点降低，合金高温下压缩强度降低程度越来越大。     

Al对AlxMo0.5NbTiVSi0.2高熵合金组织和性能影响

采用真空电弧熔炼工艺制备了不同Al含量的Al_xMo_0.5NbTiVSi_0.2(x=0.5,0.8,1.0,摩尔比)难熔高熵合金。研究了合金的相组成、微观组织、密度和力学性能。结果表明,Al_xMo_0.5NbTiVSi_0.2高熵合金的微观组织为典型的树枝晶结构,均由BCC固溶体相和M₅Si₃金属间化合物相组成。Al含量的增加并未使得合金的相组成发生改变。合金BCC基体相富集Al、Mo和V元素,M₅Si₃相富集Ti和Si元素,Nb元素在两相中分布较为均匀。随Al含量增加,合金的密度从6.18 g/cm³降至5.86 g/cm³,硬度提升了13.7%,压缩屈服强度增加约332 MPa,增幅达到37%,抗压强度从1 073 MPa提高到1 457 MPa,断裂应变从13.6%增加到14.4%。合金力学性能的提升主要是通过固溶强化、细晶强...     

新型NixTi24Zr12Nb10Ta12Mo5W5高熵合金含能结构材料的组织及力学性能

设计并使用真空电弧炉制备了Ni_xTi₂₄Zr₁₂Nb₁₀Ta₁₂Mo₅W₅(x=5, 10, 15, 20, 32, 35)高熵合金含能结构材料。采用XRD、EPMA、万能试验机等手段研究了不同Ni含量下合金的相组成、微观组织及力学性能。结果表明,随着Ni含量增加,合金的微观组织由BCC1+BCC2+Ni₁₀Zr₇+Unknown四相结构转变为BCC1+BCC2+Ni₁₀Zr₇+Unknown+FCC五相结构;当x=20时合金呈现出最佳的强塑性匹配,屈服强度为1 653 MPa,压缩伸长率约为19%;随着Ni含量增加,合金硬度先升高后降低,当x=20时合金硬度(HV)达到最大值为592。     

高屈强比Ti-Nb-Cr-V-Zr系难熔高熵合金的组织与力学性能

通过真空电弧熔炼法制备了Ti_47-xNb₂₃Cr₁₈V₁₂Zr_x(x=0、4、8、12 at%)系难熔高熵合金,随后在1200℃下保温12 h对合金进行均匀化热处理。利用X射线衍射(XRD)、扫描电镜(SEM)、万能力学试验机和显微硬度仪等研究了铸态与均匀化热处理态合金的相组成、微观组织及力学性能。结果表明：Zr元素的添加使铸态合金在枝晶间析出C15结构的Cr₂(Ti, Nb, V,Zr)-Laves相,同时,Zr元素含量的增加增强了合金的压缩屈服强度和硬度,但使其塑性降低。均匀化热处理并未改变合金的相组成,但使合金的组织形貌发生了明显改变,并大大增加了析出相的体积分数。经过均匀化热处理后,合金的强度和硬度有所降低,但塑性得到改善。其中,Ti₄₃Cr₁₈Nb₂₃V₁₂Zr₄合金的压缩塑性由铸态时的29%提升至超过50%,同时具有1110 MPa的屈...     

应变速率对HCP/FCC双相CoCrFeNiNb0.5高熵合金力学性能的影响(英文)

利用分离式霍普金斯压杆、扫描电子显微镜和透射电子显微镜研究应变速率对铸态CoCrFeNiNb_0.5高熵合金力学行为的影响。CoCrFeNiNb_0.5高熵合金由先共析密排六方(HCP)相和共析组织构成，合金的共析结构为片层状的HCP相和片层状的面心立方(FCC)相。当应变率从1×10^-4 s^-1增加至6×10³ s^-1时，合金的屈服强度不会显著增加；然而，合金的破坏应变剧烈降低。片层状HCP相的准静态塑性变形机理为缠结状位错的增殖，而其动态塑性变形机理转变为剪切。片层状HCP相的剪切变形能够导致CoCrFeNiNb_0.5高熵合金在低压缩应变(ε=0.1)下形成微裂纹。由于片层状HCP相中微裂纹的数量随着动态压缩应变的提高而增加，微裂纹的扩展引发材料的雪崩式断裂。因此，铸造态CoCrFeNiNb_0.5高熵合金表现出显著的应变速率诱发脆性特性。     

Zn对Mg-10Gd-2Y-0.5Zr镁合金组织和性能的影响

通过在Mg-10Gd-2Y-0.5Zr合金中添加Zn,采用SEM、XRD及万能拉伸试验机,研究了Zn添加对其铸态组织和力学性能的影响。结果表明,Mg-10Gd-2Y-0.5Zr合金的铸态组织主要由α-Mg、Mg₅(Gd,Y)和Mg₂₄(Y,Gd)5相组成,而添加质量分数为0.5%~1.5%的Zn后,合金的铸态组织主要由α-Mg、Mg₅(Gd,Y,Zn)、Mg₂₄(Y,Gd,Zn)₅及Mg₁₂(Gd,Y)Zn相组成。添加0.5%的Zn后,合金的室温力学性能明显提高,当Zn含量高于1.0%后,镁合金的室温力学性能开始逐步降低。当Zn含量为0.5%时,合金具有较佳的综合力学性能,其抗拉强度、屈服强度和伸长率分别为197 MPa、160 MPa和4.37%。Zn对Mg-10Gd-2Y-0.5Zr合金铸态力学性能的影响与其铸态组织中Mg₅(Gd,Y,Zn)、Mg₂₄(Y,Gd,Zn)₅和Mg₁₂(Gd,Y)Zn第二相及其数量有关。     

热处理对Al2O3f/Mg-6Al-0.5Nd-0.5Gd复合材料组织及硬度的影响

采用金相显微镜、维氏硬度测试仪及扫描电镜等,研究热处理工艺对Al₂O_3f /Mg-6Al-0.5Nd-0.5Gd复合材料微观组织及硬度的影响。结果表明,固溶处理后β-Mg_l7A1₁₂相大部分固溶于α-Mg基体中,而稀土化合物Al₂Nd、Al₂Gd相因其高熔点,在试验温度下不能分解与固溶,Al₂O_3f纤维变得细小均匀,Mg₂Si相呈一定的分解、球化趋势。时效处理使β-Mg_l7A1₁₂相再次析出,呈层片状或弥散颗粒状分布,优化了其铸态时粗大的网状结构,此时,复合材料硬度达到最大值,比铸态时提高了47.5%。     

淬火温度对Nd1.5Mg0.5Ni7储氢合金相结构的影响

通过对不同温度淬火的Nd₂Ni₇和Nd_1.5Mg_0.5Ni₇样品粉末进行X射线衍射分析(XRD)和扫描电子显微镜/能谱分析(SEM/EDS),研究了Nd_1.5Mg_0.5Ni₇合金淬火后的相结构。结果表明,淬火后,Nd_1.5Mg_0.5Ni₇三元合金主要由Ce₂Ni₇型相和Gd₂Co₇型相组成;淬火温度对合金主相晶格常数几乎没有影响;Mg的加入促进了低温相的形成,并减少了杂质相的生成。     

含β"-Mg5Si6相Al-Mg-Si合金深冷环境强塑双增原子级机理(英文)

采用分子动力学方法研究β″-Mg₅Si₆析出相体积分数及深冷温度对Al-Mg-Si合金纳米力学特性的影响。模拟结果表明，与纯Al的峰值应力相比，当温度为77 K、β″析出相体积分数为0.107时，Al-Mg-Si合金的峰值应力提高97.05%。当β″析出相体积分数为0.107时，与300 K下样品的峰值应力相比，在27 K下该样品的峰值应力可提高23.55%。研究结果表明，深冷环境有助于提高总位错密度，使样品能够承受更大的应力，这为含β″相的Al-Mg-Si合金提供额外强度和韧性。降低温度可以明显抑制孔洞的萌生和生长(生长率27 K时下降88.5%)，从而提高Al-Mg-Si合金的塑性。     

超声振动对含LPSO结构的Mg98Y1.0Ni0.5Al0.5合金显微组织与力学性能的影响(英文)

低Y、Ni含量的LPSO结构增强镁合金具有低成本、优异力学性能的特点。为进一步提升其综合力学性能,掺杂Al元素及熔体超声振动处理是可行的途径。通过扫描电子显微镜、能谱分析、透射电子显微镜、X射线衍射和纳米压痕测试研究掺杂Al元素后低Y、Ni含量的Mg98Y1.0Ni0.5Al0.5合金的显微组织,对比超声振动对显微组织与力学性能的影响。掺杂Al后LPSO结构的含量降低,且在块状LPSO结构相邻处析出圆整的Al₂NiY相。Al₂NiY相与LPSO结构和Mg基体在界面处均不共格。通过对熔体施加超声振动处理后,Al₂NiY相被有效细化为短片状,并均匀分布在基体中,阻碍微裂纹的产生和扩展,从而提高Mg₉₈Ni_0.5Y_1.0Al_0.5合金的力学性能。与未经超声处理Mg₉₈Ni_0.5Y_1.0Al_0.5合金相比,其极限抗拉强度和伸长率提升至187 MPa和7.9...     

Synthesis and characterization of Al2O3-Ce0.5Zr0.5O2 powders prepared by chemical coprecipitation method

Al₂O₃-Ce_0.5Zr_0.5O₂ catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al³⁺ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce_0.5Zr_0.5O₂ powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al₂O₃ formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m²/g) was larger than that of ACZ-M (62.1 m²/g) and Ce_0.5Zr_0.5O₂ (17.1 m²/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al₂O₃, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al₂O₃. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce_0.5Zr_0.5O₂ powders.     

Role of Al2O3 layer in oxidation resistance of Cu-Al dilute alloys pre-annealed in H2 atmospheres

Copper was alloyed with small amounts of Al (0.2, 0.5, 1.0 and 2.0 mass%) to improve the oxidation resistance. Copper (6 N) and the Cu-Al alloys were oxidized at 773-1173 K in 0.1 MPa oxygen atmosphere after hydrogen annealing at 873 K. Continuous very thin Al₂O₃ layers were formed on the surface of all Cu-Al dilute alloys during the hydrogen annealing. Oxidation resistance of Cu-Al alloys was improved especially for Cu-2.0Al at 773-973 K, while it decreases on increasing the oxidation temperature. Cu-Al alloys followed the parabolic rate law at 1173 K, but most of other cases do not at and below 1073 K. Oxidation resistance for Cu-Al alloys was found relevant to the maintenance of the thin Al₂O₃ layer at the Cu₂O/Cu-Al alloy interface.     

DEFORMATION BEHAVIOR AND CONSTITUTIVE EQUATION FOR Zr55Cu30Al10Ni5 BULK METALLIC GLASS IN SUPERCOOLED LIQUID REGION

Zr₅₅Cu₃₀Al₁₀Ni₅块体非晶合金(BMG)在过冷液态区内的单向压缩实验表明: 材料在过冷液态区内的形变行为强烈依赖于温度和变形速率. 随着应变速率的增加, 材料的流变特征由Newtonian流变转变为非Newtonian流变.利用扩展指数本构方程模型建立了非晶合金的流变应力、应变速率和温度的关系.     

保温时间对瞬时液相扩散连接的Ti3Al /Ti2AlNb接头微观结构及力学性能的影响

采用Ni-Ti复合箔片作为中间层,在990 ℃、低连接压力（0.1 MPa）下,通过瞬时液相（TLP）扩散连接制备了Ti₃Al/Ti₂AlNb异种合金接头。分析了保温时间（10~90 min）对Ti₃Al/Ti₂AlNb接头微观结构及力学性能的影响,并研究了TLP扩散连接接头的界面演变和形成机制。结果表明,Ti₃Al/Ti₂AlNb接头具有典型的“Ti₃Al | Al_0.5Nb_0.5Ti₃ | 残余 Ni | NiTi | NiTi₂ | 残余 Ti | Al_0.5Nb_0.5Ti₃ | Ti₂AlNb”多层梯度结构。随着保温时间的延长,接头的抗剪切强度先增大后减小,当保温时间达到60 min时,Ti₃Al/Ti₂AlNb接头的抗剪切强度最大,达到167±12 MPa。另外,接头的断裂主要发生在Ti₂AlNb/Ti附近的NiTi₂层,并向Ti层延伸,呈现出脆性断裂的特征。     

Reactive sintering study of a novel cemented carbide hard alloy (W0.5Al0.5)C0.5-Ni

Cemented carbides hard alloy (W_0.5Al_0.5)C_0.5-13.3 vol% Ni was successfully prepared by reactive sintering of carbon, nickel powder and W_0.5Al_0.5 alloy powder. The novel cemented carbide hard alloy has superior mechanical properties. The influence of sintering time and temperature on the microstructure, mechanical properties and density of the specimens are well described. Interestingly, both sintering time and temperature have amazing influence on the mechanical properties, density and microstructure of the specimen. During the reactive sintering process, Ni was the binder phase for sintering (W_0.5Al_0.5)C_0.5-Ni cemented carbide, and it also accelerated the reaction rate of synthesizing (W_0.5Al_0.5)C_0.5. The reactive sintering is a good method for preparing cemented carbide hard alloy (W_0.5Al_0.5)C_0.5-Ni. Another phenomenon is that no WNi/W₃Ni₃C/NiC_x type phases are found in the bulk specimens, although it was prepared by reactive sintering the carbon, nickel powder and W_0.5Al_0.5 alloy powder directly and the carbon vacancy reach to the astonished 50% value.     

Thermal stability of bulk Zr2Al4C5 ceramic at elevated temperatures

Thermal expansion analysis is applied to the study of phase segregation of Zr₂Al₄C₅ at elevated temperatures (20-2000 °C) under flowing argon. Such information would be useful for the detection of phase decomposition temperature and thermal stability of materials. The detected phase-decomposition temperature of Zr₂Al₄C₅ is approximately 1900 °C. The presented thermal expansion analysis results are in good agreement with the X-ray diffraction (XRD) and SEM results. The results indicate that Zr₂Al₄C₅ is susceptible to decomposition through sublimation of high vapor pressure of Al and weaker covalent bonds between ZrC slabs and Al₄C₃ layers. Thus, minimal amounts of Al, Zr₂Al₃C₅, Al₄C₃ and ZrC form on the surface layer. Zr₂Al₃C₅ further decomposes to ZrC_1 − x and Al₄C₃ at 2000 °C. However, the amount of decomposing phase slowly increases, and the structural shape of bulk Zr₂Al₄C₅ ceramic is always kept stable during heat treatment.     

Structure and shape memory effect in a Ni54Mn25Ga20Gd1 alloy with a high transformation temperature

Ni₅₄Mn₂₅Ga₂₀Gd₁ (at.%) alloy with a high transformation temperature has been obtained by substituting 1 at.% Gd for Ga in a ternary Ni₅₄Mn₂₅Ga₂₁ shape memory alloy. The microstructure and phase transformations in the Ni₅₄Mn₂₅Ga₂₀Gd₁ alloy have been investigated by SEM, TEM, XRD and DSC. The results show that the microstructure of the Ni₅₄Mn₂₅Ga₂₀Gd₁ alloy consists of matrix and hexagonal Gd (Ni,Mn)₄Ga phase, and martensitic transformation start temperature (M_s) is 491 K. The compressive strength and the compressive strain are about 958 MPa and 16%, respectively. The complete recovery is obtained from the Ni₅₄Mn₂₅Ga₂₀Gd₁ alloy as the pre-strains are no more than 3%. The maximum shape memory strain is achieved in Ni₅₄Mn₂₅Ga₂₀Gd₁ alloy with pre-strain of 4%, and the shape memory strain and recovery ratio are 1.9% and 87.5%, respectively. The two-way shape memory effect is also observed in Ni₅₄Mn₂₅Ga₂₀Gd₁ alloy.     

Characterization of sol-gel synthesised lead-free (1 − x)Na0.5Bi0.5TiO3-xBaTiO3-based ceramics

The crystal structure, microstructure, dielectric and ferroelectric properties of (1 − x)Na_0.5Bi_0.5TiO₃-xBaTiO₃ ceramics with x = 0, 0.03, 0.05, 0.07 and 0.1 are investigated. A structural variation according to the system composition was investigated by X-ray diffraction (XRD) analyses. The results revealed that the synthesis temperature for pure perovskite phase powder prepared by the present sol-gel process is much lower (800 °C), and a rhombohedral-tetragonal morphotropic phase boundary (MPB) is found for x = 0.07 composition which showing the highest remanent polarization value and the smallest coercive field. The optimum dielectric and piezoelectric properties were found with the 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃ composition. The piezoelectric constant d₃₃ is 120 pC/N and good polarization behaviour was observed with remanent polarization (P_r) of 12.18 pC/cm², coercive field (E_c) of 2.11 kV/mm, and enhanced dielectric properties ?_r > 1500 at room temperature. The 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃-based ceramic is a promising lead-free piezoelectric candidate for applications in different devices.     

Synthesis and electrochemical performance of Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 with core-shell structure as cathode material for Li-ion batteries

The core-shell structure cathode material Li(Ni_0.8Co_0.15Al_0.05)_0.8(Ni_0.5Mn_0.5)_0.2O₂ (LNCANMO) was synthesized via a co-precipitation method. Its applicability as a cathode material for lithium ion batteries was investigated. The core-shell particle consists of LiNi_0.8Co_0.15Al_0.05O₂ (LNCAO) as the core and a LiNi_0.5Mn_0.5O₂ as the shell. The thickness of the LiNi_0.5Mn_0.5O₂ layer is approximately 1.25 μm, as estimated by field emission scanning electron microscopy (FE-SEM). The cycling behavior between 2.8 and 4.3 V at a current rate of 18 mA g⁻¹ shows a reversible capacity of about 195 mAh g⁻¹ with little capacity loss after 50 cycles. High-rate capability testing shows that even at a rate of 5 C, a stable capacity of approximately 127 mAh g⁻¹ is retained. In contrast, the capacity of LNCAO rapidly decreases in cyclic and high rate tests. The observed higher current rate capability and cycle stability of LNCANMO can be attributed to the lower impedance including charge transfer resistance and surface film resistance. Differential scanning calorimetry (DSC) indicates that LNCANMO had a much improved oxygen evolution onset temperature of approximately 251 °C, and a much lower level of exothermic-heat release compared to LNCAO. The improved thermal stability of the LNCANMO can be ascribed to the thermally stable outer shell of LiNi_0.5Mn_0.5O₂, which suppresses oxygen release from the host lattice and not directly come into contact with the electrolyte solution. In particular, LNCANMO is shown to exhibit improved electrochemical performance and is a safe material for use as an electrode for lithium ion batteries.     

Al2O3/ZrO2涂层在热等静压致密化TiAl基合金粉末过程中对碳钢包套的影响

由于焊接性能好,成本低,碳钢材料常被用于制作热等静压致密化TiAl基合金粉末的包套。在高温高压下,碳钢包套和TiAl基合金粉末通过原子扩散在扩散区形成脆性相,导致包套失效,并降低TiAl基合金压坯的致密度。为了确保碳钢包套在热等静压致密化TiAl基合金粉末过程中的可靠性,本文利用热喷涂的方法在20#钢包套内壁添加了Al2O3/ZrO2（A-Z）涂层,然后在 。在热等静压试验中,带有A-Z涂层的20#钢包套用于热等静压致密化Ti-46Al-2Cr-2Nb-(W, B)预合金粉末,其工艺为：1523K,2.5小时,130MPa+1603K,0.5小时,130MPa。为了对比,利用没有A-Z涂层的20#钢包套在1523K,3小时,130MPa的工艺参数开展了热等静压致密化试验。利用扫描电镜、电子探针等设施对获得的压坯进行了观测和分析。结果表明：A-Z涂层的加入可以防止脆性金属间化合物的形成。在热等静压过程中,20#钢包套中的Fe原子无法通过扩散的方式与TiAl基合金中的钛原子和铝原子相遇。因此,20#钢包套在热等静压过程中的可靠性得到了保证。此外,通过利用添加A-Z涂层的钢包套获得了完全致密的TiAl基合金压坯。压坯呈现出了近全片层类型的微观组织,其室温下的抗拉强度和延伸率也分别突破了590MPa和2.0%。