Alternative microstructures and their influence on mechanical properties of case-hardened gears

Forschung im Ingenieurwesen - Case hardening is one of the most common heat treatment processes for highly loaded shafts and gears. Due to numerous investigations, a microstructure...     

工艺参数对自增强HDPE棒材的力学性能和微观结构的影响

通过口模挤出工艺获得了自增强HDPE棒材,通过SEM观察、X射线分析、DSC分析以及力学性能测试,研究了工艺参数对挤出自增强HDPE棒材微观结构和力学性能的影响.研究结果表明,与普通模压试样相比,自增强试样内部有大量的微纤结构和串晶互锁结构,结晶度获得提高.挤出温度对材料性能影响最大,挤压比次之,口模温度对材料性能影响最小.当挤出温度为130℃,口模温度为0℃,挤压比为15时,自增强HDPE棒材的力学性能最佳,其拉伸强度和弯曲强度分别为220.6和152.9MPa.     

Study on microstructures and mechanical properties of short-carbon-fiber-reinforced SiC composites prepared by hot-pressing

Short-carbon-fiber-reinforced silicon carbide composites were prepared by hot-pressing with SiC powder, Polycarbosilane as precursor polymer and MgO–Al₂O₃–Y₂O₃ as sintering additives. The phase composition, microstructure and mechanical properties of the composites with different Polycarbosilane content were investigated. The results showed that, dense composites could be prepared at a relatively low temperature of 1800 °C via the liquid-phase-sintering mechanism and the highest mechanical property was obtained for the composites with 20 wt.% PCS and 8 wt.% sintering additives. The amorphous interphase formed during sintering process in the composites not only contributed to the densification of the composites, but also improved the fiber–matrix bonding. The nano-silicon carbide derived from Polycarbosilane, could also play a role of improving the relative density of the composites.     

碳对高温钛合金Ti-60组织和性能的影响

在Ti-60合金中碳的加入量大于0.17%时,组织中析出TiC结构的碳化物.在α β相区再结晶,碳偏聚于初生α(αp)相,导致碳化物主要在β转变组织中析出,其析出的百分数取决于αp体积分数.在β相区热处理,析出的碳化物钉扎β原始晶界,阻碍β晶粒的长大.β晶粒尺寸D、碳化物颗粒直径d和体积分数f三者遵循D/d∝f-1/3关系.随着碳含量的增加,β晶粒尺寸减小,α'片层通过界面迁移迅速长大以及形成α片层的合金元素的扩散速度加快,导致α'或α片层的厚度增加.碳的加入量小于0.09%时,碳完全固溶于基体中,产生固溶强化,β晶粒细小,导致合金的强度和蠕变抗力提高.碳含量增加导致粗大碳化物颗粒的析出,变形时产生应力集中使合金的塑性和蠕变性能降低.     

Effect of cerium on microstructures and mechanical properties of AZ61 wrought magnesium alloy

The effects of Cerium (Ce) addition on microstructures and mechanical properties of hot-extruded AZ61 alloy were investigated. It is found that Ce refines Mg₁₇Al₁₂ particles and brings about precipitation of a new rod-like phase that is identified as Al₄Ce by X-ray diffraction. During hot deformation, Al₄Ce particles can refine dynamic recrystallized grains by impeding grain growth. For Ce additions up to 1.0 wt%, the recrystallized grain size decreases; When Ce addition is more than 1.0 wt%, grain size increases inversely. Strength and elongation of extruded or annealed specimens at room temperature increase along with Ce addition up to 1.0 wt%, then decrease. Optimal mechanical properties are correspondent to 1.0 wt% Ce addition.     

变形制度对低碳锰钢组织性能的影响

为了获得细晶铁素体/贝氏体的复相组织,通过控轧控冷工艺研究了低碳锰钢在奥氏体区变形时变形量、终轧温度和卷取温度对组织演变和力学性能的影响规律.研究表明,增加变形量(对应道次间隔时间缩短)可以细化铁素体晶粒,但当终轧温度降低到800℃时,变形量的增加以及开冷温度的降低不利于贝氏体组织的获得.通过调整变形量、终轧温度、可开冷温度并适当降低卷取温度,可使实验钢获得晶粒尺寸约为5μm的铁素体和10%~20%的贝氏体组织,低碳锰钢强塑性能良好.     

Influence of Y on microstructures and mechanical properties of high strength steel weld metal

A comprehensive investigation is conducted into the effect of yttrium oxide on microstructures of weld metal deposits and mechanical properties of high strength steel electrode measured in the Ni–Cr–Mo–V alloy system. The results demonstrate a gradual decrease of the content of proeutectoid ferrites and a gradual increase of acicular ferrites, as the content of yttrium oxide increases from 0% to 0.02%. However, as the content of yttrium oxide surpasses 0.02%, the content of acicular ferrites reduces significantly. Meanwhile, the toughness under low-temperature impact increases and then decreases, as the content of yttrium varies from 0% to 0.03%, reaching the maximum of 102J at the field of 0.02%. However, the strength fails to change significantly. The results also indicate that the cold cracking sensitivity is lower when the content of yttrium oxide is 0.02%, but the values would increase as the content of yttrium oxide fluctuates.     

Effect of heat treatment on microstructures and mechanical properties of Al/Fe bimetal

The Al/Fe bimetallic castings were prepared by the compound casting combined with hot-dip galvanising and aluminising, and the effect of the heat treatment on microstructures and mechanical properties of the Al/Fe bimetallic castings was systematically studied in the present work. The thickness of the reaction layer of the Al/Fe bimetallic castings continuously increased with increasing solution temperature or prolonging solution time. However, the excessive solution temperature and solution time promoted cracks of the reaction layer. Regardless of as-cast or heat treatment, there were respectively the Fe₂Al_5, Al₉Fe₄Si_3, FeAl_3, Al₈Fe₂Si and Al_4.5FeSi phases in the reaction layers. The nano-hardnesses of the reaction layer after heat treatment exhibited an increase compared to that of the as-cast condition.     

微量稀土元素对Q235B钢组织和性能的影响

为研究微量稀土元素对Q235B钢的夹杂物形态转化和细晶化及钢材强韧性能的影响,用真空感应炉熔化、精炼、制备了不同微稀土质量分数的钢样,用成分、OM、SEM、EDS和图像分析仪等方法,分析研究了微量稀土元素对Q235B钢微观组织和力学性能的影响.结果表明：在本研究条件下,随稀土量的增加,铁素体晶粒由24μm减小至12μm...     

Studies of microstructural and mechanical properties of Nylon/Glass composite Part II The effect of microstructures on mechanical and interfacial properties

This is a part of a series of studies on the influence of thermal processing on microstructures and mechanical properties of thermoplastic composites. In this paper, the effect of cooling rate during thermal moulding processes on the mechanical properties of bulk unidirectional commingled yarn GF/PA6 composites (Iosipescu shear strength, transverse flexural tensile strength and elastic modulus) has been investigated. Cooling rate from fast to slow, –60°C/min, –3°C/min and –1°C/min, were achieved at 1.5 MPa pressure. Scanning electron microscopy (SEM) was used to analyse the damaging mechanisms of the fracture surfaces of the tested samples. The different dynamic responses of the samples were observed by polarised optical microscopy (POM) during the mechanical tests. The results indicated that when the cooling rate was varied from fast to slow, the interfacial tensile and shear strength were improved associated with enhanced elastic modulus. These results may be attributed to the slow cooling achieved a high transcrystallinity between the glass fibres and PA6 matrix, and high crystallinity of phase in the PA6 matrix.     

The mechanical properties and microstructures of copper and brass joints soldered with eutectic tin-bismuth solder

The mechanical properties and microstructures ofcopper and brass soldered with eutectic tin-bismuth solder have been determined and the joints examined using metallographic techniques. Joints made with copper were stronger than those made with brass. At the copper/solder interface a uniform layer 2m thick of Cu_5.2Sn₅ was formed and at the brass/solder interface a uniform layer 2 m thick of (Cu, Zn)_2.9Sn and an irregular layer 2 to 5m thick of (Cu, Zn)_5.7Sn₅ were formed. Copper joints fractured etthocopper/solder interface and brass joints fractured in the internmetalic layer. Copper joints soldered with eutectic Sn-Bi were stronger than copper joints soldered with eutectic Sn-Pb and the reverse was true for brass joints. Results are also given for the effect of thermal shock on copper and brass joints soldered with Sn-Bi and Sn-Pb solders, and also for We fatigue and creep behaviour of joints soldered with eutectic Sn-Bi solder.     

Solidification microstructures and mechanical properties of vertical centrifugal cast high speed steel

Abstract

This study was undertaken to investigate the influence of Nb and V alloying elements and manufacturing conditions on the microstructural behaviour and mechanical characteristics of HSS (high speed steel) roll manufactured by a VCC (vertical centrifugal casting) process. In the Fe - 2C - 6Cr-1.5W - 3Mo - 4V alloy, the amount of MC carbide was increased and the the amount of M₇C₃ carbide decreased with an increase in V and Nb content. In steel containing 3%Nb, primary NbC carbide was formed within the cell in the matrix. The hardness of steel containing 6.5%V but no Nb was increased a little but when 9%V was added, the hardness decreased in the specimen owing to the soft ferritic matrix. The hardness of the matrix in steel containing 1.5%Nb increased, but decreased for 3%Nb addition. In wear tests, wear loss decreased with increasing rotational wear speed.     

少量Sc对7055铝合金组织与性能的影响

利用拉伸试验、光学金相、X射线物相分析、SEM及TEM等实验方法,研究了添加0.2%Sc(质量分数)对7055铝合金组织与性能的影响.实验结果表明,添加0.2%Sc可以显著细化7055铝合金铸态晶粒并减少晶界非平衡共晶相数量,促进非平衡共晶相在均匀化退火时的溶解,从而提高合金固溶度;由于Sc的添加可以提高7055Sc合金的溶质原子固溶度、形成更为均匀弥散分布的Al3ScZr粒子、以及抑制变形组织再结晶和有效细化固溶处理后的(亚)晶粒尺寸,因而显著提高7055Sc合金综合力学性能.     

Effect of sintering temperature on microstructures and mechanical properties of spark plasma sintered nanocrystalline aluminum

Organic-coated aluminum nano-powders were consolidated by spark plasma sintering technique with low initial pressure of 1 MPa and high holding pressure of 300 MPa at different sintering temperature. The effect of sintering temperature on microstructures and mechanical properties of the compact bulks was investigated. The results indicate that both the density and the strain of the nanocrystalline aluminum increase with an increase in sintering temperature. However, the micro-hardness, compressive strength and tensile stress of the compact bulks increase initially and then decrease with increasing sintering temperature. The nanocrystalline aluminum sintered at 773 K has the highest micro-hardness of 3.06 GPa, the best compressive strength of 665 MPa and the supreme tensile stress of 282 MPa. A rapid grain growth of nanocrystalline aluminum sintered at 823 K leads to a decrease in micro-hardness, compressive strength and tensile stress. After annealing, a remarkable increase in strain and a slight rise in strength were obtained due to the relief of the residual stress in nanocrystalline Al and the formation of composite structure.     

Effect of solidification on microstructures and mechanical properties of carbon nanotubes reinforced magnesium matrix composite

A novel approach was successfully developed to fabricate bulk carbon nanotubes (CNTs) reinforced Mg matrix composites. The distribution of CNTs in the composites depends on the solidification rate. When the solidification rate was low, CNTs were pushed ahead of the solidification front and will cluster along grain boundaries. When the solidification rate was high, CNTs were captured by the solidification front, so the CNTs remained inside the grain. Moreover, good interfacial bonding was achieved in the composite under high solidification rate. Meanwhile, compared with the matrix alloy, the ultimate tensile strength (UTS) and yield strength (YS) of the composite were significantly improved. The mechanical properties of the composite under higher solidification rate are better than composite under low solidification rate and the alloy. Moreover, most CNTs on the fracture surfaces were directly pulled out from the matrix. The Kelly–Tyson formula agreed well with the experimental tensile value in the composite under higher solidification rate, and the load-transfer efficiency is almost equal to 1.     

The effect of milling conditions on microstructures and mechanical properties of Al/MWCNT composites

Strengthening efficiency of multi-walled carbon nanotubes (MWCNTs), depending on their morphology and interface structure, is investigated for aluminum-based composites. The composites were fabricated by hot-rolling the powders which were ball-milled under various conditions. Milling variables affect the dispersion, dimension and interface structure of MWCNTs. With an insufficient milling intensity, MWCNTs are mostly located on the surface of powder, exposed to severe impact, and readily damaged. As the milling intensity increases, MWCNTs are embedded inside the powder and then dispersed through plastic deformation of the powder. Furthermore, aluminum infiltrates the core of MWCNTs during milling, increasing the diameter of MWCNTs. The outer surface of the Al-infiltrated MWCNTs sticks to the matrix, providing a strong interface by mechanical interlocking. The Al-infiltrated MWCNTs exhibit superior strengthening efficiency. On the other hand, the composite with unfilled MWCNTs, fabricated with a higher milling intensity, exhibits better ductility and pull-outs of the tubes in tensile fracture.     

Effects of synthesis technology route on mechanical properties and phases/microstructures of polyurethane elastomers

Abstract

In the present paper, the synthesis technology of polyurethane elastomers was studied with an aim at better controlling their phases/microstructures and properties. In particular, mechanical properties and glass transition temperatures as well as microphase separation of different polyurethane elastomers synthesised by four technology routes, with an emphasis on the effects of raw materials and their feeding sequences, were investigated using a universal testing machine, a differential scanning calorimetric (DSC) and a fourier transform infrared spectrometer (FITR). The results offered an ideal synthesis route: first diisocyanate was added into the dried polyether, then the two materials were fully reacted and finally the chain extender was added into the mixture products. The resulting polyurethane elastomer exhibited an excellent mechanical performance, a low glass transition temperature and a perfect microphase separation.     

Effects of TiO/Al ratio on microstructures and mechanical properties of TiAl base composites

Effects of TiO₂/Al ratio on the microstructures and mechanical properties of in situ Al₂O₃/TiAl based composites were investigated. The results indicate that the as-sintered products consist of grains of nearly lamellar ?₂ + ? structure with a dispersion of randomly oriented Al₂O₃ particles. A 43.9Ti-38.6Al-17.5TiO₂-nNb₂O₅ system was compared to 57.46Ti-36.78Al-5.76TiO₂-nNb₂O₅ system. The lamellar spacing of the products increases and the ?₂ phase volume decreases with decreasing TiO₂/Al ratio. For each system, as the volume of ?₂ phase increases, the average lamellar spacing decreases. Strength increases with an increasing TiO₂/Al ratio due to the amount of ?₂ phase. Al₂O₃ phase increases with increasing TiO₂/Al ratio. Toughness increases with decreasing TiO₂/Al ratio. When the Nb₂O₅ content is smaller than 6 wt.%, the lamellar spacing plays an important role in toughness than the Al₂O₃ content. When the Nb₂O₅ content is larger than 6 wt.%, the Al₂O₃ content exhibits significantly increases the values of toughness than lamellar spacing.     

析出相对深冲DP钢组织性能及织构的影响

为了研究析出相对深冲DP钢织构的影响机制,采用Thermo-calc热力学软件计算DP钢的平衡析出相,并利用SEM、TEM与XRD等手段分析了两种不同成分的DP钢组织性能与织构演变.研究表明:试验钢的主要析出相为MC_SHP、M₇C₃、MnS和AlN;与低Mo钢相比,高Mo钢的奥氏体区被缩小,且MoC的析出温度更高,铁素体晶内与沿晶界形成了大量的纳米级MoC析出;860 ℃退火后,高Mo钢中形成了约3%的均匀弥散分布的马氏体,抗拉强度达到445 MPa,r值为1.5,而低Mo钢发生了贝氏体相变,各项力学性能明显降低;两种试验钢的热轧板织构较弱,冷轧后{223}<110>取向密度稳定增加,退火后均形成了强烈的γ纤维织构,而低Mo钢中{001}<110>织构是导致其r值偏低的主要原因.