Effects of homogenization temperature on microstructure and mechanical properties of high-speed-extruded Mg–5Bi–3Al alloy

This study investigates the effects of billet homogenization temperature on the dynamic recrystallization behavior during high-speed extrusion and resultant microstructure and tensile properties of the Mg–5Bi–3Al(BA53,wt%)alloy.Two billets homogenized at 350 and450℃(350H and 450H billets)are extruded at a high speed of 69 m/min.The 350H billet has a relatively smaller grain size and a higher abundance of fine Mg3Bi2particles compared to the 450H billet.During extrusion of the 350H billet,enhanced dynamic recrystallization occurs as a result of its finer grains and abundance of particles,while the growth of recrystallized grains is suppressed by the grain-boundary pinning effect of particles.Ultimately,the extruded 350H material is characterized by smaller grains,relatively greater number of Mg3Bi2particles,and a higher internal strain energy than the extruded 450H material.The tensile strength of the extruded 350H material is higher than that of the extruded 450H material owing to stronger grain-boundary hardening,particle hardening,and strain hardening effects.The extruded 350H material also exhibits a higher tensile elongation as its smaller grains inhibit the formation of crack-inducing undesirable twins during tension.The results from this study demonstrate that a decrease in the homogenization temperature from 450 to 350℃leads to improved strength and ductility in the high-speed-extruded BA53 material.

Dynamic Constitutive Model of Physical Simulation in High-Speed Blanking for C5191 Phosphor Bronze

Strain hardening,strain rate strengthening and thermal softening data of C5191 phosphor bronze at highspeed blanking are not easy to be obtained with a general measure method,therefore,it is quite difficult to establish the dynamic constitutive model.To solve this problem,the tensile properties at a strain rate of 1 s^(-1) by GLEEBLE-3500,and dynamic tensile conditions at strain rates of 500,1 000 and 1 500 s^(-1) by split Hopkinson tensile bar (SHTB) apparatus are studied.According to these test data,the classic Johnson-Cook equation is modified.Furthermore,the modified Johnson-Cook equation is validated in the physical simulation model of high-speed blanking.The results show that the strength of C5191 phosphor bronze maintains a certain degree of increase as the strain rate increasing and presents a clear sensitivity to strain rate.The modified Johnson-Cook equation,which has better description accuracy than the classical Johnson-Cook equation,can provide important material parameters for physical simulation models of its high-speed blanking process.

两种不同加工状态CrCoNi中熵合金的微观组织和力学性能研究

中熵合金是近年来材料研究的热点,一般对中熵合金采用“铸造-轧制-热处理”的加工工艺。采用XRD、金相显微镜、万能试验机、扫描电镜对铸态、轧制+热处理的CoCrNi中熵合金的金相组织、硬度、室温、低温(77 K)力学性能以及拉伸断口进行分析。结果表明:对铸态CoCrNi合金轧制+热处理,两种不同状态合金均稳定保持面心立方(FCC)相,其中铸态组织为典型的树枝晶,但是无明显第二相存在,轧制+热处理对铸态组织有明显的细化和均匀化作用,对材料的拉伸强度和硬度有明显提升。两种不同加工状态的合金在低温下拉伸性能均发生明显提升,其中轧制后热处理中熵合金在液氮温度下抗拉强度达到1262.9 MPa、拉伸延伸率能达到89.6%,且两种状态下中熵合金在不同温度下均发生塑性断裂。在室温下CoCrNi合金的塑性变形行为以滑移为主,低温下CoCrNi合金塑性变形行为以孪生为主。

低成本Fe_(60)(CoCrNiMn)_(40)富铁中熵合金的显微组织与性能

通过增加CoCrFeMnNi合金中的铁含量,制备了低成本富铁中熵合金Fe_(60)(CoCrNiMn)_(40)(原子分数/%),对其进行了1200℃×3 h均匀化处理、轧制和900℃×1 h退火处理,研究了该合金的显微组织、拉伸性能及耐腐蚀性能等。结果表明:试验合金由面心立方结构的单一奥氏体相组成,再结晶晶粒大小均匀,平均晶粒尺寸约为17.8μm,再结晶晶粒内出现退火孪晶;试验合金在室温下表现出优异的拉伸性能和应变硬化能力以及在NaCl溶液中显著的自钝化行为和优异的耐腐蚀性能,其抗拉强度为603 MPa,屈服强度为226 MPa,断后伸长率为81.6%,在NaCl溶液中的自腐蚀电位为-0.4616 V,自腐蚀电流密度为2.74×10^(-6) A·cm^(-2),电荷转移电阻为2.94×10^(5)Ω·cm^(2);与其他富铁多组分合金相比,试验合金的抗拉强度和断后伸长率更大,塑性应变高出10%以上,自腐蚀电流密度更低。试验合金的拉伸断口由均匀分布的韧窝组成,拉伸断裂方式为韧性断裂;在NaCl溶液中电化学腐蚀后,试验合金表面出现明显腐蚀坑,电化学腐蚀方式主要为点蚀。

VNbTa难熔多主元合金的低温力学性能研究

通过拉伸测试,研究了等原子比体心立方结构VNbTa中熵合金的低温变形行为。结果表明,该合金具有优异的低温应变硬化能力,这导致其有27%的断裂伸长率的同时抗拉强度高达1930 MPa。微观结构演化分析揭示,变形过程形成的扭折带及{112}<111>变形孪晶有效调节了剪切应变,促进了合金塑性和强度的提高。此外,螺型位错缠结、位错带及位错带的交互也对合金强度和加工硬化能力有重要贡献。因此,VNbTa中熵合金优异的低温力学性能归因于{112}<111>变形孪晶、扭折带、螺型位错滑移及交互的协同作用。

电子元器件粘接用单组分环氧胶的制备与性能研究

针对电子元器件粘接用途,制备了单组分中低温固化环氧胶粘剂。主要研究了不同类型环氧树脂、填料以及固化促进剂对其拉伸剪切强度、拉伸强度、断裂伸长率和固化性能的影响。研究结果表明:以双酚F型环氧树脂为基础聚合物制备的单组分环氧胶粘剂,相对于双酚A型及聚氨酯改性型环氧树脂,显示出更优的粘接强度及较低的硬度;搭配碳酸钙使用时,拉伸剪切强度较硅微粉、高岭土明显提升,且断裂伸长率达到约55%,具有一定的弹性;采用相同量的促进剂,固化促进速率依次为改性脲促进剂>改性胺促进剂>咪唑促进剂;开发的单组分环氧胶粘剂产品在常温下可正常存放3周,使用方便,兼具良好的固化效率,力学性能优异,可应用于电子元器件的结构粘接。

Effect of Heat Sink and Cooling Mediums on Ferrite Austenite Ratio and Distortion in Laser Welding of Duplex Stainless Steel 2205

In order to control the ferrite and austenite percentage in duplex stainless steel welding, many researchers try to change the laser welding parameters and cooling medium, but ignore to study the influence of heat sink effect on weld strength. In this work, the effect of aluminium heat sink and varying cooling medium on the laser welding of duplex stainless steel (DSS) 2205 is studied. The 2 mm thick DSS sheets welded with pulsed Nd: YAG laser welding machine by varying the cooling medium (air and oil) and an aluminium plate used as a heat sink. The welded specimens tested for tensile strength, micro-hardness, distortion, microstructure and radiography analysis. The faster cooling rate in the oil quenching process enhances the ferrite percentage compared with air-cooled samples. But the faster cooling rate in oil quenching leads to more distortion and using aluminium as a heat sink influenced positively the distortion to a small extent. The lower cooling rate in air quenching leads to a higher tensile strength of the welded specimen. The objective of this work is to analyse experimentally the effect of cooling medium and heat sink in the mechanical and metallurgical properties of laser welded duplex stainless steel.

Evaluation of Mechanical Properties of Medium Carbon Steel Quenched in Water and Oil

Samples of medium carbon steel were examined after heating between 900℃ - 980℃ and soaked for 45 minutes in a muffle furnace before quenching in palm oil and water separately. The mechanical behavior of the samples was investigated using universal tensile testing machine for tensile test and Vickers pyramid method for hardness testing. The microstructure of the quenched samples was studied using optical microscope. The tensile strength and hardness values of the quenched samples were relatively higher than those of the ascast samples, suggesting improved mechanical properties. However, samples quenched in palm oil displayed better properties compared with that of water-quenched samples. This behavior was traced to the fact that the carbon particles in palm oil quenched samples were more uniform and evenly distributed, indicating the formation of more pearlite structure, than those quenched in water and the as-received samples.

Ductile Fracture Characterization for Medium Carbon Steel Using Continuum Damage Mechanics

This paper presents the ductility characterization for a medium carbon steel, for two microstructural conditions, that has been evaluated using the continuum damage mechanics theory, as proposed by Kachanov and developed by Lemaitre. Tensile tests were carried out using loading-unloading cycles in order to capture the gradual deterioration of the elastic modulus, which may be linked to the ductile damage increase with increasing plastic strain. The mechanical parameters for the isotropic damage evolution equation were obtained and then used as inputs for a plasticity-damage coupled nu- merical algorithm, validated through numerical simulations of the experimental tensile tests. A comparison between the SAE 1050 steels studied and two carbon steel alloys (obtained from the literature), provided some basic understanding of the influence of the carbon level on the evolution of the damage parameters. An empiric relationship for this set of parameters, which can provide useful data for preliminary studies envisaging prediction of ductile failure in carbon steels, is also presented.

搪玻璃压力容器用热轧中厚Q245R钢板的性能

采用箱式炉模拟热轧正火态20 mm厚Q245R钢板的高温烧成。检测了钢板的微观组织、拉伸性能、冲击性能和氢穿透时间(t_(H2))。结果表明:模拟高温烧成的钢板表层、1/4和1/2厚度处的微观组织与正火态类似,由带状珠光体和铁素体组成,烧成前后钢板的铁素体晶粒尺寸无明显变化;模拟高温烧成前后钢板的屈服强度、抗拉强度没有明显变化,断后伸长率升高,0℃冲击韧性下降,但均满足标准要求;正火态钢板表层、1/4和1/2厚度处的t_(H2)为2.70~4.35 min/mm^(2),远低于钢板双面或全表面涂搪玻璃要求的6.7 min/mm^(2)临界值,且从钢板表面至中心的t_(H2)值有明显差异;随着钢中碳质量分数的降低和珠光体体积分数的减少,玻璃层中气泡的数量和直径减小,有利于提高玻璃层质量。

基于电磁加载的新型中应变率动态拉伸测试系统与试验方法

以轻金属和复合材料为代表的新型航空航天结构材料在中应变率环境下的动态力学行为和相关失效机理研究受到越来越多的关注。为了充分探究新型结构材料性能与应变率之间的对应关系,在电磁铆接系统的基础上研发了一种可以实现中应变率动态拉伸测试的新型试验系统,为金属和复合材料及其连接结构进行动态性能测试提供了一种科学高效的试验方法。首先介绍了电磁加载装置的基本原理和功能特点,分别对加载系统、控制系统和数据采集系统进行了详细说明;其次介绍了动态加载测试过程不同参数下对应力学响应的变化及其重复试验下的一致性结果,进而验证了整个测试系统的稳定性和可靠性;最后采用该系统测试了不同应变率下2024–T6铝合金的力学特性。测试结果表明,电磁加载动态拉伸测试系统可以准确地反映出应变率变化对2024–T6铝合金性能的影响,这为新型航空材料进行服役环境下的结构安全性研究提供了有力的技术支撑。

安钢中温压力容器钢15CrMoR开发

采用冶炼、真空精炼及高效化连铸获得洁净度高的钢水和质量优良的压力容器钢15CrMoR铸坯;经炉卷机组轧制、热处理机组正火加回火处理,15CrMoR成品钢板各项力学性能和工艺性能均较稳定,满足GB/T 713-2014标准要求。热轧态钢板组织为铁素体、珠光体和少量贝氏体,经正火加回火处理后,成品钢板高温拉伸强度富裕40~70 MPa,组织为铁素体加珠光体,高温性能优良。

水合条件对血管内导管力学性能影响的研究

血管内导管,如中心静脉导管(CVC)、经外周静脉置入中心静脉导管(PICC)、输液港导管(PORT)是临床治疗中不可或缺的医疗器械。由于导管功能的不同及临床血液环境的复杂性,在人体内留置的时间也不尽相同,其最长可达一年之久。因此,研究水合条件对血管内导管力学性能的影响,对指导企业生产及临床使用具有重要现实意义。文章重点对不同浸泡时间、浸泡介质下聚氨酯导管、硅橡胶导管的峰值拉力进行数据对比分析,结果表明:浸泡介质对血管内导管峰值拉力的影响不显著,浸泡时间对不同材料血管内导管峰值拉力的影响差异较大。与硅橡胶导管相比,浸泡时间对聚氨酯导管峰值拉力的影响较显著,在浸泡2 h~180 d时间段,随着浸泡时间的增长,聚氨酯导管的峰值拉力呈现减小的趋势。

聚碳酸酯中应变率拉伸力学特性试验研究

对聚碳酸酯板材进行了准静态和中应变率下的单向拉伸试验,结果表明:聚碳酸酯材料在中、低应变率条件下呈现明显的非线性变形特征、应变率强化效应及高速韧性特征。基于试验结果,建立了聚碳酸酯材料在中应变率下的屈服应力-应变率近似关系方程,采用一个非线性弹簧和一个Maxwell体的粘弹性模型分析了聚碳酸酯材料拉伸力学性能的应变率相关性,得到了中应变率下聚碳酸酯材料的本构方程,方程预测结果与试验结果一致性良好,能够为材料设计使用提供有力支撑。

张拉荷载下全长粘结锚杆工作机理试验研究

三峡永久船闸闸室的高、薄混凝土衬砌墙由高强结构锚杆与闸室岩体联结,单根锚杆在工程运行期所受最大张拉荷载可能达到600 kN,薄混凝土衬砌墙能否提供足够的锚固力,以及混凝土的受力和破坏状态如何,是工程中非常关心的问题。以三峡工程问题的现场试验为依托,在回答工程问题的同时,着重讨论了在受张拉荷载作用下全长粘结锚杆的工作机理,指出了锚杆在轴向受拉过程中,受锚杆螺纹的影响,锚杆与粘结介质之间将产生法向剪胀变形,对保障和提高锚杆的锚固力具有特别重要的意义。还对全长粘结锚杆的设计理论、提高锚固效果的措施进行了讨论。

聚碳酸酯板材中、低温本构模型的建立

通过拉伸实验及参数辨识建立了聚碳酸酯中低温DSGZ本构方程（-50℃～60℃），研究了聚碳酸酯板材在不同温度（-50、-20、0、20、60℃）及应变率（0．0006、0．006、0．06、0．12s^-1）下的力学性能．研究结果表明：普通DSGZ模型无法确切描述聚碳酸酯应变软化行为．在此基础上，引入了修正的DSGZ模型，结果表明：修正DSGZ模型可更加有效地描述聚碳酸酯板材中、低温的力学行为．

木醋杆菌生产细菌纤维素发酵条件优化

以从中国普通微生物菌种保藏管理中心购买的木醋杆菌(CGMCC 1.1812)作为初始菌种,对液体发酵生产细菌纤维素的发酵条件进行了优化.结果标明,最佳培养条件为:70 g L1蔗糖、12 g L1酵母膏、28 g L1胰蛋白胨、2.7 g L1Na2HPO4、2 g L1KH2PO4、1 g L1柠檬酸钠、2 g L1MgSO4、pH6.0、于500 mL三角瓶50 mL装液量静置培养6 d.在此条件下进行培养,细菌纤维素干重产量可达9.678 g L1.并对其性质进行了研究,纤维素含水率在95%~98%之间,拉伸强度为1.91 MPa.

热处理对中频感应重熔NiCrBSi涂层抽油光杆性能的影响

采用火焰热喷涂-中频感应重熔技术在20CrMo抽油光杆基体表面制备NiCrBSi涂层并进行热处理,采用扫描电镜、显微硬度计、X射线应力测试仪、万能试验机和疲劳试验机等仪器,研究了热处理工艺对涂层光杆组织、硬度、表面应力、力学性能和疲劳性能等方面的影响。结果表明,中频感应重熔NiCrBSi涂层的制备和热处理对光杆基材表层组织、硬度和表面应力影响较大,热处理温度对涂层的硬度影响不显著;涂层制备和热处理会显著降低杆体的疲劳性能,重熔处理工艺的抗拉强度最大但塑性指标很差,并在疲劳试验中出现典型脆性断口,高温热处理工艺可以使涂层光杆获得较好的拉伸力学性能;普通20CrMo抽油光杆以磨损、腐蚀和疲劳断裂为主要失效原因,而NiCrBSi涂层/20CrMo光杆疲劳性能的显著降低可能成为其失效的主要原因。

热喷涂纳米β-SiC/LBS涂层的吸波性能

应用喷雾造粒技术对纳米β-SiC/LBS复合吸波粉末进行团聚造粒,采用超音速火焰喷涂工艺制备高温纳米复合吸波涂层,并对复合涂层性能进行研究。结果表明,颗粒状β-SiC弥散在半熔融状态的LBS中形成涂层。涂层与基体的结合强度为8.46MPa,拉伸过程中,涂层从内部撕裂,并表现为脆性断裂。与普通陶瓷吸波涂层相比,复合涂层的吸波性能得到扩展;随着涂层厚度的增加,复合涂层对电磁波的衰减能力将从高频向低频移动。受到涂层抗拉强度的限制,复合涂层的厚度应该小于1mm。纳米β-SiC含量(质量分数)为46%时,复合涂层的电磁波反射率系数达到-13dB;当在涂层厚度相同而微波频率大于14GHz时,复合涂层的电磁波反射率系数均小于-10dB。数值模拟结果表明,当β-SiC质量含量为46%时,复合涂层的吸波性能最佳。

抽油杆疲劳性能实验分析

目的有效地预防和减少因抽油杆断裂导致的油井修井作业,进一步降低油田开发成本。方法采用岛津电液伺服疲劳试验机,对D级和H级抽油杆进行材质成分分析,测试力学性能、空气和腐蚀介质下疲劳强度、拉压载荷对疲劳性能的影响,并进行对比分析。结果H级抽油杆的力学性能优于D级抽油杆。随着含水量的增加,两种抽油杆的抗疲劳性能均降低,在空气中,H级抽油杆的疲劳性能均优于D级抽油杆。在腐蚀环境中,D级抽油杆的疲劳性能优于H级抽油杆,并且两种抽油杆所受拉压载荷对疲劳均有一定影响。结论含水是影响抽油杆腐蚀疲劳性能的关键因素,H级抽油杆应在低含水区块应用,D级抽油杆在中高含水区块应用。抽油杆中和点以下产生的附加拉应力是导致抽油杆偏磨的直接原因,在中和点以下应优化扶正防磨设计。在中高含水区块,应加大对服役年限较长抽油杆的更换力度,以减少和预防抽油杆断裂事故的发生。