不同压力温度条件下聚合的Si-Ni-B中介聚晶金刚石(PCD)抗压强度及组织特征研究

在一系列高温超高压条件下,制备了Si-Ni-B中介结合的聚晶金刚石(PCD),用压缩试验、X射线衍射分析、SEM、金相分析研究了PCD聚合的温度、压力条件对其抗压强度及组织特征的影响。     

合金微结构的调整对铁基块体金属玻璃室温塑性的影响(英文)

报道一种新奇的现象,即随着Fe75Mo5P10C8.3B1.7块体金属玻璃的直径从1.5mm增加到2.0mm,其室温压缩塑性反而从0.5%增加到1.8%。这主要归因于随着铁基块体金属玻璃样品直径的增加,原位形成了零星的α-Fe枝晶相,这种在边缘化的块体金属玻璃中出现的异质结构是提高当前铁基块体金属玻璃室温塑性的主要原因。     

An investigation of cold extruding hollow flanged parts from sheet metals

Hole flanging with cold extrusion can avoid necking or fracture as encountered in conventional sheet metal-forming operations. Substantial flange height and lip thickness can be achieved with flange extrusion because the forming load is compressive. Using a hydraulic press, flange extrusions of 5 and 10 mm inner diameters were produced in pieces of cup-shaped galvanized steel, as well as aluminum 5052 workpieces with a thickness of 0.8 mm, both of which had a pre-hole on the cup bottom. As the punch load was exerted on the cup rim, a clamping force was applied to suppress dilation on the cup bottom.The experiments showed that with sufficient clamping force, significant flange height could be extruded. The utmost extruded flange of 5 mm i.d. was 6 times larger than that drawn from the conventional method, whereas that of 10 mm i.d. was 3.8 times larger than that drawn from the conventional method. However, no flange was extruded and buckling occurred on the cup bottom when the clamping force was insufficient. The experiments confirmed the results predicted by the FE simulation. For a selected flange inner diameter, the ratio of the extruded flange height to the increase in cup bottom thickness was directly related to the normalized clamping pressure, i.e. the ratio of clamping pressure to workpiece yield strength. Therefore, both the application of a larger clamping force or the use of low-strength workpiece materials facilitated the extrusion of flange while suppressing the dilation of the cup bottom. Flange extrusions with a larger diameter correspond to a smaller extrusion ratio or reduction of area. Experiments showed that a significant flange height could be extruded with a 10 mm inner diameter for both galvanized-steel and aluminum 5052, while results for extrusions with a 5 mm inner diameter were unfavorable when using galvanized-steel. High-strength materials and a high extrusion ratio required greater clamping force for the flange extrusion process, and consequently caused excessive forming load on the forming dies as well as on the hydraulic press, thus rendering the process less effective.     

Cu50 Zr42 Al8块体金属玻璃的组织和力学性能

采用悬浮熔炼-铜模吸铸法制备了Cu50Zr42Al8块体金属玻璃,研究了其楔形试样的组织演变.随着熔体凝固过程中冷却速度的变化,楔形试样中存在表面全非晶区,中心晶体区以及二者之间的过渡区域,并确定Cu50Zr42Al8块体金属玻璃临界尺寸为4.8 mm.分别考察了φ4 mm铸态完全非晶棒和φ5 mm非晶复合棒的力学性能.φ4 mm非晶棒的压缩断裂强度,弹性应变和塑性应变分别为2260 MPa,2.0%,0.4%,几乎没有塑性变形.而φ5 mm铸态非晶复合棒的屈服强度、断裂强度分别为1670MPa、1849 MPa,弹性应变和塑性应变分别为1.6%和1.9%.非晶基体中存在的马氏体相CuZr和正交晶相Cu10Zr7的竞争影响了非晶复合棒的最终力学行为.     

喷丸对铝合金亚表面裂纹闭合修复的影响与试验

目的 研究喷丸修复7075-T651铝合金亚表面裂纹的愈合机理及修复效果。方法 建立材料亚表面裂纹在喷丸作用下的修复模型,运用Ansys进行数值模拟计算,并预测裂纹深度修复阈值;根据模型,利用线切割制造相应的裂纹,并对其进行喷丸修复,从残余应力、疲劳强度、微观结构等方面分析裂纹愈合的机理,并评估修复效果。结果 仿真结果表明,在弹丸直径D=0.5 mm、弹丸速度v=100 m/s时喷丸修复效果最佳,裂纹修复深度阈值为0.15mm;裂纹修复区域的表面应力为非裂纹区域的83.17%,实验结果与仿真结果相符;在修复裂纹后,试件的疲劳强度可以达到完好试样的70.32%。剧烈的喷丸冲击使裂纹亚表面材料产生较大的微观形变热,有利于组织形变,促使裂纹两侧的晶粒组织形成闭合挤压,宏观上表现为压应力下组织的紧密闭合,这种闭合起到了修复裂纹的作用,整体上属于物理性修复,但仍无法完全消除裂纹对材料的消极影响。结论 喷丸通过压力作用对亚表面材料的裂纹进行闭合修复,使材料的疲劳强度得到恢复,这对于铝合金结构件裂纹的早期修复和应急性修复具有积极作用。     

BT25钛合金在锻造过程中失稳变形和动态再结晶行为的数值模拟

分别利用失稳图和功率耗散图确定BT25钛合金失稳变形组织和动态再结晶变形组织的热力参数边界条件,并将其输入到Deform-3D有限元软件中,使加工图技术与有限元技术能够进行有效结合。利用二次开发后的软件对BT25钛合金在变形温度为950~1100 ℃和应变速率0.001~1 s^-1的条件下进行失稳变形组织和动态再结晶行为的模拟和预测,并通过对比金相组织,验证了该模拟结果的可靠性。结果表明,流动应力随变形温度的升高或应变速率的降低而降低;失稳变形组织集中在低温、高应变速率区域;高温和低应变速率均有利于动态再结晶（DRX）行为;微观组织的观察结果与模拟预测的结果吻合较好,说明本研究提出的加工图技术与有限元技术相结合的方法对模拟与预测金属锻造过程中的失稳变形组织和DRX行为是可行的。     

某洗衣机内筒用430不锈钢锈蚀原因分析

通过金相显微镜组织观察、扫描电镜微观形貌观察以及X射线能谱仪成分分析等手段对洗衣机内筒用430不锈钢锈蚀原因进行分析。研究结果表明，试样表面锈蚀是由于钢板冲孔处变形程度大，导致试样表面的钝化膜减薄或者破坏，严重降低了不锈钢的耐蚀性，由工况环境中的氯离子活化作用进而引发锈蚀；缺陷处锈蚀程度的不同，其表面铬铁氧化物中氧含量也不同。在生产过程中应避免试样长期处于潮湿介质中，可有效防止残留氯离子破坏表面钝化膜，显著降低锈蚀缺陷的发生。     

某洗衣机内筒用430不锈钢锈蚀原因分析

通过金相显微镜组织观察、扫描电镜微观形貌观察以及X射线能谱仪成分分析等手段对洗衣机内筒用430不锈钢锈蚀原因进行分析。研究结果表明,试样表面锈蚀是由于钢板冲孔处变形程度大,导致试样表面的钝化膜减薄或者破坏,严重降低了不锈钢的耐蚀性,由工况环境中的氯离子活化作用进而引发锈蚀;缺陷处锈蚀程度的不同,其表面铬铁氧化物中氧含量也不同。在生产过程中应避免试样长期处于潮湿介质中,可有效防止残留氯离子破坏表面钝化膜,显著降低锈蚀缺陷的发生。     

钎焊工艺对75Ni8排锯钢基体性能影响的研究

探究钎焊工艺对75Ni8排锯钢钎焊后力学性能和显微组织的影响。实验共选用7种钎料进行感应钎焊,借助力学试验机、冲击试验机、维氏硬度计、金相显微镜等进行力学性能和显微组织分析。结果表明:三明治HL861钎焊接头的剪切强度最高,为164.87 MPa;CT737冲击韧性最高,为50.08 J/cm2;距离钎缝近的母材区域维氏硬度下降较快,最低为1 176 MPa,原始母材的维氏硬度为4 468.91 MPa;金相观察发现:距离钎缝近的区域母材组织粗大,而原始母材组织细小均匀。75Ni8排锯钢钎焊后的组织和性能受温度影响较大,当加热时间变长,回火温度超过600℃时,组织转变为回火屈氏体。      

Microstructure of shear-induced thixoformed Al-4.5Cu-1.5Mg alloy via RAP and SSTT processes

In this research, the effect of the thixoforming temperature on the microstructure and mechanical properties was investigated in the thixoforming of the feedstock produced by the RAP(recrystallization and partial melting) and SSTT(semi-solid thermal transformation) processes for Al-4.5Cu-1.5Mg alloy. In the RAP process, the percentage reduction in area was approximately 35%. Thixoforming was done at 610, 620, and 630 °C. Globular microstructure was observed at all temperatures and conditions. The minimum average globule size was 39 μm, and it was obtained in the thixoforming of the feedstock produced by the RAP process in the section of 4 mm in diameter at 620 ° C after applying shear. Its corresponding compressive strength was-877.44 MPa. The maximum average globule size was 136 μm, and it was obtained in the thixoforming of the feedstock produced by the SSTT process in the section of 10 mm in diameter at 630 °C before applying shear. Its corresponding compressive strength was-769.18 MPa. The finest and most spherical globules, as well as the highest compressive strength were obtained at 620 °C in both RAP and SSTT states.     

抽拉速率对螺旋选晶器选晶行为和晶体取向演变的影响

采用宏观-微观耦合的元胞自动机（CAFE）方法,研究了不同抽拉速率对螺旋选晶器的选晶行为和晶体取向演变的影响,并通过实验对仿真结果进行了验证。结果表明：在相同的抽拉速率下,随着与激冷面距离的增大,枝晶数目逐渐减少,一次枝晶臂间距逐渐增大。随着抽拉速度由2 mm/min增加到8 mm/min,一次枝晶臂间距逐渐减小,枝晶茎数增加,枝晶间距逐渐减小,枝晶组织逐渐细化。在模拟过程中,在螺旋选择器启动块的3种抽拉速率下,固态组织的数量、面积和颜色都是相似的;在螺旋部分,在5 mm/min提取速率下晶体的微结构数量比其他2个提取速率下的少,并且面积更大,颜色更浅。从选晶器的晶粒组织演变和金相组织分析结果可以得出,中等抽拉速率（5 mm/min）下选晶器的选晶效率优于其他2种抽拉速率。     

大功率风力发电机齿轮失效分析

国内某厂生产的大功率风力发电机,其增速齿轮箱中的高速中间轴运行大约1 000 h后发生断裂失效.为探究断裂失效的原因,对断裂齿轮先后进行宏观形貌观察、电子探针形貌分析、金相组织分析、硬度检验、烧伤检验等分析.宏观检测下齿面破损较严重,在某些齿根附近轮齿几乎全部剥落;微观下观察,齿面在破损后仍旧长时间运行,无明显断口特征...     

铸造温度对Zr_(53.9)Cu_(29.4)Ni_(4.9)Al_(9.8)Fe_2块体金属玻璃力学性能和组织的影响(英文)EI北大核心CSCD

在水冷铜坩埚中采用铜模吸铸法以不同的铸造温度制备出直径3mm的Zr53.9Cu29.4Ni4.9Al9.8Fe2合金试样,研究了铸造温度对锆基块体金属玻璃力学性能和组织的影响。研究结果表明,对于试样的非晶结构,存在一个临界铸造温度,低于此温度会有晶体相析出。在一定范围内提高铸造温度可以提高锆基块体金属玻璃的压缩断裂强度和轻微降低塑性。当铸造电压升高至9kV时,不但可以提高合金试样的压缩断裂强度,同时提高其塑性,其塑性达到2.62%。通过控制与自由体积和残余应力相关的铸造温度,可以调节锆基块体金属玻璃的力学性能。     

冷却速率对Zr61.6N16.6Cu13.8Al8非晶合金力学性能的影响

采用铜模吸铸法制备了阶梯形的Zr61.6N16.6Cu13.8Al8非晶合金，利用x射线衍射（XRD）分别对不同直径的合金试样进行结构分析，利用万能试验机及扫描电镜对试样进行压缩试验和断口形貌分析。研究表明，由于冷却速度的影响，合金试样直径为3mm时是非品结构；直径为4mm和6mm时晶体相增多，甚至为完全晶体相结构；对于Zr61.6N16.6Cu13.8Al8合金，直径为3mm时的断裂强度可达到1703MPa，塑性变形可达到1．7％，适当体积晶体相的加入可以有效提高非晶材料的塑性。     

316L不锈钢的低能量激光冲击强化工艺

以316L不锈钢作为模型材料,系统研究了低能量高重频激光冲击强化工艺。建立了激光光斑覆盖率概念,对于直径d为0.4~0.8 mm 间的光斑,其饱和覆盖率在6~7之间。在此饱和覆盖率条件下,机械手移动速率v与光斑直径d的匹配关系为v=70d。最大残余压应力随着光斑直径的减小而增大,当光斑直径d为0.4 mm时获得最大残余压应力为662 MPa,残余压应力影响层深度为565 μm。激光冲击强化区域表面粗糙度未明显增加,但与未冲击区域存在一定高度台阶。在1.59 GW/cm²激光功率密度下,该台阶高度为23 μm。     

Mechanical Behavior and Microstructural Development of 6063-T1 Aluminum Alloy Processed by Equal-Channel Angular Pressing (ECAP): Pass Number Influence

Equal-channel angular pressing (ECAP) is a very interesting method for modifying the microstructure in producing ultrafine-grained materials and nanomaterials. It consists mainly of pressing test samples through a die containing two channels that are equal in cross section and intersect at a certain angle. As a result of pressing, the sample theoretically deforms by simple shear and retains the same cross-sectional area to allow repeat pressing for several cycles. A 6063-T1 aluminum alloy was investigated in this study. The specimens were processed for up to nine passes (one, three, six, and nine ECAP passes, respectively) using a die channel angle of 90°. After ECAP, the samples were cut from each specimen and prepared for metallographic analysis and mechanical testing. The microstructures of the ECAP treated and as-received material were investigated using both optical microscopy and scanning electron microscopy. All samples (ECAP processed and as-received) were mechanically investigated in compression tests. Ultimate compressive strength, yield strength, and compression modulus were obtained. Also, all ECAP processed specimens were investigated for microhardness and compared with the as-received material.     

滚压有限元模型数值模拟

滚压数值模拟是制定滚压工艺、预测滚压后工件表面残余应力分布,以及判定工件疲劳性能的重要工具。目前的滚压数值模拟主要集中在对曲轴以及回转体的分析,少有的对平面滚压数值模拟中,大多数也只分析了单圈或不到一圈的滚压过程,而且与实际滚压工艺存在较大的区别。为弥补以上不足,该文采用有限元商业软件ABAQUS提供的Explicit模块,并结合python编程语言,开发了更接近于实际的滚压模拟过程;采用该模型研究了滚压力的大小、滚针直径、表面摩擦系数等对于残余应力分布规律的影响,并通过H13钢的滚压实验,对模型模拟结果进行了验证。     

40Cr钢梯形丝杠经感应加热调质的工艺质量分析

本文通过金相、显微硬度等方法对Ф110mm40Cr钢梯形丝杠的感应加热调质样品进行了检验与分析。结果表明,该40Cr钢梯形丝杠样品的整体组织并非正常的回火索氏体,局部存在板条状回火马氏体形态,而且硬度较常规调质的偏高。因此,该工件的质量不符合工艺设计要求,原因是感应加热时回火不充分所致。     

6082铝合金MIG焊焊接接头组织与力学性能研究

通过拉伸、弯曲、硬度试验以及金相分析等对6082铝合金MIG焊接头的力学性能与显微组织进行了研究。结果表明:采用5087焊丝焊接6082铝合金时,具有较好的抗拉性能,板厚8和4mm的焊接接头焊态的抗拉强度分别为母材的77.8%和73%;弯曲断裂集中在熔合线处,弯曲角度均较小;6082铝合金MIG焊接头焊缝中心组织为等轴晶,靠熔合线的焊缝晶粒沿散热方向呈柱状晶,熔合区晶粒粗大;软化区出现过时效效应,使Mg2Si长大,成为接头最薄弱的区域。     

金相样品制备及其对显微组织评判的影响

通过对金相试样制备过程的试验研究,总结了取样、镶嵌、磨制、抛光、侵蚀及制样过程的各个步骤的操作方法,指出了在金相样品制备过程中的不当操作会对显微组织分析产生不良影响。