Mo-Si合金室温及高温拉伸力学性能研究

采用粉末冶金技术制备了不同Si含量(0,0.1,0.3wt%Si)的Mo-Si合金板材,并在25,300,800和1200℃下进行了静拉伸试验,研究了试验温度对Mo-Si合金板材力学性能、断裂方式及微观组织的影响。结果表明:随试验温度升高,纯钼及Mo-Si合金板材强度明显下降,但延伸率以300℃为分界点呈现出先升后降的趋势。室温下Mo-Si合金的断裂方式为穿晶解理断裂,在300及800℃时主要为韧窝延性断裂,而1200℃时为沿晶断裂。对Mo-Si合金强化机制的分析表明,室温下的强化主要来源于弥散强化和固溶强化,而在高温时,固溶作用明显减弱,颗粒弥散和粗化晶粒为主要的强化手段。     

The influence of silicon content on microstructure and hardness of Mo-Si alloys

Mo-Si alloy sheets with different silicon content were fabricated by powder-metallurgical and thermo-mechanically processing. The effect of Si content and annealing temperature on microstructure and hardness of the Mo-Si alloys were studied by using optical microscopy (OM), transmission electron microscopy (TEM) and Vickers hardness tester, respectively. The results indicated that the presence of Si can effectively refine the grain sizes and improve the hardness of Mo-Si alloys. Si can also increase the recrystallization temperature of alloys and play a significant role in restraining the grain growth at high temperatures. Increasing the annealing temperature, the microstructure of Mo-Si alloy sheets is gradually coarsened and changed from fibrous to equiaxed structure, causing reduction in hardness. The hardening effect in the Mo-Si alloys came from the refined grain strengthening, solid solution strengthening, and second phase particle strengthening, which are closely dependent on the Si content and annealing temperature.     

Influences of annealing temperature on microstructure and mechanical properties of Mo-La2O3

Influences of annealing temperature on the microstructure and mechanical properties of Mo-La₂O₃ were investigated. Effects of annealing temperature on tensile properties, fracture toughness, and microhardness are discussed. Microstructure and fracture morphology of Mo alloys are observed by optical microscope, SEM, and TEM. The results indicate that grain size increased while tensile strength, fracture toughness, and microhardness decreased with increasing annealing temperature. Larger La₂O₃ particles are located at grain boundaries or sub-boundaries, while the majority of smaller La₂O₃ particles are located within the grain. The strengthening effect is quantitatively assessed, which yielded a predicted yield strength in good agreement with measurements.     

原位反应热压复合SiCP/MoSi2的显微结构与力学性能

以Mo粉、Si粉和C粉为原料，采用湿法混合和原位反应高温热压一次复合工艺制备了不同配比的SiCp/MoSi2复合材料，研究了该种工艺原位生成的SiC颗粒对MoSi2基体显微结构和室温力学性能的影响。结果表明：原位反应生成的适量SiC颗粒可以细化基体晶粒，改善其力学性能，与同样工艺下制备的纯MoSi2相比，含40vol%SiCp的SiCp/MoSi2复合材料室温抗弯强度是其3.4倍，含50vol%SiCp的SiCp/MoSi2复合材料室温断裂韧性是纯MoSi2的1.5倍；该种工艺的强化机制为细晶强化和弥散强化，韧化机制为细晶韧化。     

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.

     

The multi-scale microstructure and strengthening mechanisms of Mo-12Si-8.5BxZr (at.%) alloys

Mo-12Si-8.5B alloys with different Zr contents (0 at.%, 1 at.%, 2 at.%, 3 at.%, 4 at.%) were manufactured via a mechanical alloying process followed by hot pressing sintering technology. The microstructure of Mo-12Si-8.5B alloy exhibited a continuous submicro- and micro-scale α-Mo matrix in which the sub-micron Mo₃Si/Mo₅SiB₂ particles were distributed. Addition of Zr to Mo-12Si-8.5B alloy promoted to form spherical nano-scale intermetallic Mo₂Zr and ZrO₂ particles, which were mainly located at the grain boundaries (GBs) as well as partially within the grains. The microstructure of Mo-12Si-8.5B-xZr alloys was remarkably refined by these Mo₂Zr/ZrO₂ nanoparticles. Additionally, results of mechanical properties indicated that the Zr addition improved the hardness, compression strength, yield strength and flexure strength of alloys. In particular, the Mo-12Si-8.5B-2Zr alloy exhibited extremely high compression strength (3.38 GPa), yield strength (3.17 GPa) and flexure strength (1.15 GPa). Quantitative analyses indicate that both fine-grained strengthening and Zr-rich particle strengthening mechanisms play a significant role in strengthening the Mo-Si-B-Zr alloys, the strengthening is dominantly governed by grain size reduction. Furthermore, Zr getters detrimental oxygen by synthesizing ZrO₂ distributed at grain/phase boundaries, which contributes to increasing the GBs cohesion. Fracture surfaces revealed that the fracture mode transformed from intergranular to transgranular fracture owing to Zr addition.     

Influence of Initial Microstructure on the Strengthening Effect of Extruded Mg–8Sn–4Zn–2Al Alloys

The Mg–8Sn–4Zn–2Al(TZA842, in wt%) alloys with different initial microstructure(as-cast-AC and homogenization treatment-HT) subjected to hot extrusion. Also, the strengthening responses to AC and HT for the extruded TZA842 alloys were reported. The results revealed that the alloy subjected to HT shows finer grain size, more homogenous microstructure and weaker basal texture than those of counterpart subjected to AC. In addition, compared with TZA842-AC alloy, precipitates were finer and uniformly dispersed in TZA842-HT owing to the utilization of HT. Moreover, the TZA842-HT alloy showed higher yield strength of 200 MPa, ultimate tensile strength of 290 MPa and elongation(EL) of17.9% than those of TZA842-AC, which was mainly attributed to the combined effects of grain boundary strengthening,precipitation strengthening, solid solution strengthening and weak texture. Strengthening mechanism for both alloys was discussed in detail.     

ZrO2对钼铼合金微观组织与性能的影响

钼铼合金具有优良的力学性能和机加工性能,是电子、核工业等领域关键的结构材料。在钼铼合金中加入氧化锆,形成弥散强化作用,并结合形变强化来提高材料的力学性能。研究发现,合金粉粒度随着ZrO₂含量的增加而减小,在含量为0.7%时晶粒尺寸最细小均匀;ZrO₂颗粒在合金的变形和断裂过程中表现出钉扎效应,显著提升合金的抗拉强度、屈服强度和断后延伸率等力学性能;ZrO₂强化钼铼合金的抗拉强度和断后延伸率在ZrO₂含量为0.7%时达到最高值,随后减少;ZrO₂基本弥散分布在晶界处并与钼基体形成良好结合界面,可以抑制晶界的迁移,提高钼合金的变形抗力。     

Influence of zirconium content on microstructure and creep properties of Mo–9Si–8B alloys

Mo–Si–B alloys with a molybdenum solid solution accompanied by two intermetallic phases and Mo₅SiB₂ are a prominent example for a potential new high temperature structural material. In this study the influence of 1, 2 and 4 at.% zirconium on microstructure and creep properties of Mo–9Si–8B (at.%) alloys produced by spark plasma sintering is investigated. Creep experiments have been carried out at temperatures of 1100 °C up to 1250 °C in vacuum. The samples exhibit sub-micron grain sizes as small as 450 nm due to the chosen production route. With addition of 1 at.% zirconium, formation of SiO₂ on the grain boundaries can be prevented, thereby enhancing grain boundary strength and creep properties significantly. Moreover ZrO₂ particles also enhance creep resistance of the molybdenum solid solution. Creep deformation is a combination of dislocation creep in the grains including dislocation-particle interaction and grain boundary sliding leading to intergranular fracture surfaces. It is promising to use grain size adjustments in order to balance the creep and oxidation resistance of the investigated material.     

Ductilization of Mo–Si solid solutions manufactured by powder metallurgy

Mo–1.5 at.% Si alloys with additions of either Y₂O₃ or Zr were manufactured by mechanical alloying. The Y₂O₃ particles reduced the grain size and increased the room temperature strength, but did not alleviate the brittleness of previously investigated Mo–1.5 at.% Si without Y₂O₃. Additions of Zr, on the other hand, resulted not only in a fine grain size and an extremely high bend strength (～2 GPa), but also in limited bend ductility at room temperature. Zr additions are seen to be beneficial for three reasons. First, Zr reduces the grain size. Second, Zr getters detrimental oxygen by forming ZrO₂ particles (which in turn help to pin the grain boundaries). Third, in situ Auger analysis shows that Zr reduces the concentration of Si segregated at the grain boundaries. This is thought to enhance the grain boundary cohesive strength and thus leads to the observed ductility.     

稀土氧化镧掺杂钼合金的强化机制研究

使用粉末冶金工艺制备了不同体积分数稀七氧化镧颗粒掺杂的钼合金。观察了该合金的显微组织并测试了其力学性能。结果表明，稀士氧化镧掺杂钼合金由于其细小的氧化镧颗粒和细小的晶粒的作用而具有较高的屈服强度。对稀士氧化镧掺杂钼合金强化机制的分析结果表明，钼合金的屈服强度主要来源于三个部分：变形前基体强度、细小稀士氧化镧颗粒贡献的强度和细小钼合金晶粒贡献的强度，并给出了稀土氧化镧掺杂钼合金屈服强度与稀土氧化镧颗粒尺寸、体积分数以及晶粒尺寸之间的定量解析关系。     

挤压前的时效处理对AZ80镁合金组织和力学性能的影响

本文主要研究了挤压前的时效处理工艺对AZ80镁合金显微组织的力学性能的影响,同时结合扫描电子显微镜对断口进行分析。结果表明：挤压前时效处理可以明显细化晶粒;时效过程中析出的Mg₁₇Al₁₂粒子弥散分布在晶界处,在动态再结晶过程中起到阻碍晶界移动、阻止晶粒长大、细化组织的作用;随着时效时间的延长或者时效温度的提高,晶粒细化效果减弱;时效后进行挤压,材料的屈服强度、抗拉强度和延伸率均提高。通过对断口形貌的分析发现,早期裂纹产生于晶界处粗大的第二相周围,导致了拉伸过程中延伸率的下降。本文中挤压前时效处理对AZ80的强化效果为高性能镁合金的设计和开发提供了一种全新的思路。     

An Ultra-High Strength Over 700 MPa in Al-Mn-Mg-Sc-Zr Alloy Fabricated by Selective Laser Melting

Selective laser melting (SLM) provides optimized lightweight structures for aircraft and space applications. However, the strength of the current SLMed aluminum alloys is still lower than that of the traditional high-performance aluminum alloys. This study presents an ultra-high-strength Al-Mn-Mg-Sc-Zr aluminum alloy specifically designed for SLM by increasing the (Mg + Mn) and (Sc + Zr) content simultaneously based on the rapid solidification characteristics of the SLM process. The alloy exhibits good SLM processability with a minimum porosity of 0.23%. After aging at 300 °C, the strength of the alloy was effectively improved, and the anisotropy of mechanical properties was reduced. Additionally, the tensile yield strength and ultimate tensile strength of the alloy reached 621 ± 41 MPa and 712 ± 28 MPa, respectively; these values are superior to those of most SLMed aluminum alloys reported previously. Multiple strengthening mechanisms including solid solution strengthening, precipitation strengthening and grain refinement strengthening contribute to the high strength of the present alloys.     

Effects of Zr Content on the Microstructures and Tensile Properties of Ti-3Al-8V-6Cr-4Mo-xZr Alloys

The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-xZr(x = 0,2,4 and 6) titanium alloys were investigated.The precipitated phases and tensile fracture morphologies were observed using scanning electron microscopy and transmission electron microscopy.Experimental results show that the presence of trace impurity Si and the addition of Zr induce the formation of(TiZr)_6Si_3 silicides.The quantity of silicides increases with Zr content increasing.The dispersed silicides refined the grain size of β Zr-containing alloys,and the grain size decreases significantly with Zr content increasing.Accompanying these microstructural changes,the strength of the alloys is enhanced gradually with the increase of Zr content,which is attributed to the combination of precipitation strengthening and grain refinement.     

Correlation between microstructure and properties of fine grained Mo–Mo3Si–Mo5SiB2 alloys

Three phase α-Mo–Mo₃Si–Mo₅SiB₂ alloys of various compositions, namely Mo–6Si–5B, Mo–9Si–8B, Mo–10Si–10B and Mo–13Si–12B (at.%) were processed by a powder metallurgical (PM) route. Increasing the Si and B concentration in these Mo–Si–B alloys resulted in increasing volume fractions of the intermetallic phases Mo₃Si (A15) and Mo₅SiB₂ (T2) and the distribution of the three phases present in these alloys was dependent on the volume fractions of the individual phases. Above volume fractions of about fifty percent, bcc Mo solid solution (α-Mo) formed the matrix. Consequently, Mo–6Si–5B and Mo–9Si–8B alloys, which possessed a continuous α-Mo matrix provided increased fracture toughness at ambient temperatures. Additionally, a decreased BDTT of about 950 °C is caused by the homogeneous α-Mo matrix. In contrast, Mo–13Si–12B with 65 vol.% of the intermetallic phases that formed the matrix phase in this material had a BDTT value higher than 1100 °C, while the strength at elevated temperatures up to 1300 °C was significantly increased compared to alloys that have the α-Mo matrix. Alloy compositions with ≥50 vol.% of intermetallic phases (corresponding to alloys containing a minimum of 9 at.% Si and 8 at.% B) were oxidation resistant with minimal mass loss under cyclic conditions for 150 h at 1100 °C due to the formation of a dense borosilicate glass layer that protects the material surface.     

MA-PAS和MA-HP烧结制备的Fe_3Al金属间化合物的组织和力学性能

以机械合金化Fe-28%Al（摩尔分数）合金粉末为原料,分别采用等离子活化烧结（PAS）和热压烧结（HP）方法制备致密度高达99%的Fe3Al金属间化合物。XRD和TEM测试结果表明：PAS烧结试样保留了机械合金化粉末的A2无序结构,并呈现出亚微米晶粒区域（〉1μm）和纳米晶粒区域（〈500nm）双峰分布的特征,而HP烧结试样为部分D03有序结构,晶粒尺寸在1～2μm的范围内。压缩试验表明：在室温至800℃的条件下,采用两种方法烧结的Fe3Al金属间化合物具有近似的压缩强度,虽然当温度超过400℃后压缩屈服强度均急剧下降,但在800℃时其压缩屈服强度仍高达100MPa,远高于铸造态Fe3Al金属间化合物。相比于HP烧结和铸造态Fe3Al金属间化合物,PAS烧结Fe3Al金属间化合物表现出优异的室温塑性,其室温压缩工程应变为20%。组织结构分析和力学性能测试结果表明,超细晶无序组织有利于Fe3Al金属间化合物室温塑性和高温强度的同时增强。     

Intermediate-temperature mechanical properties of Ni–Si alloys: oxygen embrittlement and its remedies

With good corrosion resistance, reasonable room-temperature ductility, and excellent strength up to temperatures of 700 °C, Ni₃Si-based alloys show considerable potential for structural applications. The Ni–Si alloys used for acid-corrosion resistance suffer from a dynamic environmental embrittlement when tested at intermediate temperatures around 600 °C. To assess these Ni–Si alloys for elevated-temperature structural application, the mechanical properties of these alloys strengthened by Ni₃Si precipitates were systematically evaluated at different temperatures in various test environments. Oxygen was identified as the embrittling species responsible for the low ductility and premature fracture of the Ni–Si alloys. A strong dependence of elongation and fracture mode on strain rate was observed. Based on the understanding of the embrittlement mechanism, some unique approaches for improving the intermediate-temperature ductility, strength and fabricability of Ni–Ni₃Si alloys were identified: reactive element doping (such as Zr and Y) to change the grain boundary chemistry; preoxidation to form adherent oxide layers; and thermomechanical processing to tailor the grain structure/shape. Some other properties such as creep resistance and weldability of these alloys were also briefly evaluated and are discussed in this paper.     

Si-Assisted Solidification Path and Microstructure Control of 7075 Aluminum Alloy with Improved Mechanical Properties by Selective Laser Melting

The construction and application of traditional high-strength 7075 aluminum alloy (Al7075) through selective laser melting (SLM) are currently restricted by the serious hot cracking phenomenon. To address this critical issue, in this study, Si is employed to assist the SLM printing of high-strength Al7075. The laser energy density during SLM is optimized, and the effects of Si element on solidification path, relative density, microstructure and mechanical properties of Al7075 alloy are studied systematically. With the modified solidification path, laser energy density, and the dense microstructure with refined grain size and semi-continuous precipitates network at grain boundaries, which consists of fine Si, β-Mg₂Si, Q-phase and θ-Al₂Cu, the hot cracking phenomenon and mechanical properties are effectively improved. As a result, the tensile strength of the SLM-processed Si-modified Al7075 can reach 486 ± 3 MPa, with a high relative density of ~ 99.4%, a yield strength of 291 ± 8 MPa, fracture elongation of (6.4 ± 0.4)% and hardness of 162 ± 2 (HV_0.2) at the laser energy density of 112.5 J/mm³. The main strengthening mechanism with Si modification is demonstrated to be the synergetic enhancement of grain refinement, solution strengthening, load transfer, and dislocation strengthening. This work will inspire more new design of high-strength alloys through SLM.     

Microstructure and Properties of Micro-Alloyed Mg-2.0Nd-0.2Sr by Heat Treatment and Extrusion

Magnesium (Mg) and its alloys have broad application prospects in the fields such as biomedical materials and automobile manufacturing. A micro-alloyed Mg-2.0Nd-0.2Sr (wt.%) magnesium alloy is designed and obtained through semicontinuous casting. The evolution of microstructures and tensile properties are investigated with different heat treatments and extrusion treatments. The grain sizes decrease significantly after extrusion, thus changing the fracture mode during the tensile testing process. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of the properly processed extrusion alloy (referred to as MNS-E2) reach to 247 MPa, 228 MPa and 24%, respectively. The dramatical improvement of mechanical properties results from the refined grains and interactions between dislocations and precipitates. Some nanoparticle bands blocking the slippage and movement of dislocations are also found in the MNS-E2 alloy. The above causes combined result in an integrated effect of grain boundary strengthening, dislocation strengthening, precipitation strengthening and nanoparticle band strengthening. The contribution of strengthening mechanisms of MNS-E2 alloy consists of grain boundary with around 96 MPa, dislocations with around 3.4 MPa, precipitation strengthening with around 45 MPa and the nanoparticle band with around 18 MPa, respectively.