QT400—18L铸件的缩松缺陷对其力学性能的影响

通过静拉伸试验、低温冲击试验、布氏硬度试验和组织形貌分析,研究了QT400—18L球墨铸铁的缩松缺陷对其力学性能的影响。结果表明：缩松使材料的强度和塑性大幅度降低,断裂形式主要为韧性断裂;冲击断裂形式为大量解理和少量韧窝构成的混合断裂;布氏硬度值比标准硬度值至少降低9％;缩松对石墨形态、分布和材料的显微组织无明显影响。     

35CrMoV钢硬度概率分布与抗拉强度设计许用值预测分析

采用最小二乘法和K-S检验方法进行分布拟合检验,在求得35CrMoV钢硬度和抗拉强度正态分布的基础上,对其硬度和抗拉强度关系进行相关性研究,运用线性相关系数判断硬度和抗拉强度之间具有强正线性相关关系.运用正态代数运算方法,从硬度的概率分布估计抗拉强度的概率分布,预测其设计许用值,并与从抗拉强度概率分布计算得到的设计许用...     

Al-7Sn-1.1Ni-Cu-0.2Ti轴承合金微观组织与力学性能

采用扫描电镜、能谱分析、金相显微镜与WDW-100KN万能拉伸试验机研究Al-7Sn-1.1Ni-Cu-0.2Ti轴承合金的微观组织与力学性能,结合盘-销式摩擦磨损试验机考察合金不同组织状态的润滑性能。结果表明:Al-7Sn-1.1Ni-Cu-0.2Ti合金凝固收缩率为1.13%,铸态抗拉强度、屈服强度、伸长率与布氏硬度分别为191,147MPa,15.6%与34.6HBS,随着低温时效与退火热处理过程的进行,抗拉强度略有上升,屈服强度保持不变,伸长率与布氏硬度均呈现出先上升后下降的变化趋势;沿晶界分布的共晶Sn相形貌受界面张力作用逐步由板片状与骨骼状转变为层片状与短棒状,部分吸热脱溶析出在晶界处形成空腔结构,初生α-Al基体平均晶粒尺寸为182μm。与铸态和340℃退火6h相比,经175℃时效10h后,摩擦因数降低了28.6%与78.6%,体积磨损量减少了157.1%与471.4%,断口形貌以沿晶断裂与韧窝断裂为主。     

电厂锅炉末级过热器爆管原因分析

在长期过热的运行工况下,锅炉高温过热器极易产生材料的劣化以及材料组织和性能的下降,最终引发爆管事故。通过宏观检查、布氏硬度测试、抗拉强度测试和金相组织检验对某电厂末级过热器爆管原因进行分析。结果表明,该末级过热器管由于在长期高温高压下超温运行,导致碳化物在晶界富集,晶界强度下降,在拉应力的作用下,晶界产生蠕变空洞及蠕变裂纹,使得珠光体耐热钢的持久强度和抗拉强度下降,最终产生断裂失效。     

ZG06Cr13Ni4M0不锈钢材料抗拉强度与布氏硬度的关系

通过对大量ZG06Cr3Ni4Mo不锈钢材料的拉伸和布氏硬度试验数据进行统计分析,用回归分析法求出了其抗拉强度与布氏硬度之间的回归方程为HBW=0.3269Rm,并通过假设试验计算统计量F＞F临界,概率P＜0.05验证,该方程的显著性水平较高,从而可以利用该材料的抗拉强度来预测在一定置信区间内相对应的布氏硬度,为产品的...     

激光增材制造合金钢力学性能超声纵波定量无损评价

目的研究采用超声无损检测方法定量评价激光增材制造合金钢的布氏硬度和抗拉强度。方法通过搭建高精度超声纵波声时测量系统,采用脉冲反射回波法测量不同热处理状态激光增材制造24CrNiMo合金钢标定试件的超声纵波传播声时,计算超声纵波声速;在考虑激光增材制造合金钢各向异性和成形界面对超声纵波传播特性影响的基础上,研究标定试件微观组织对超声纵波声速的影响,建立标定试件激光扫描方向布氏硬度、抗拉强度、微观组织与超声纵波声速之间的映射关系。结果建立了超声纵波评价硬度及抗拉强度的标定模型,并对标定模型预测误差进行验证,硬度及抗拉强度标定模型预测误差均小于10%,满足工程应用误差指标要求。结论采用超声纵波声速可以实现激光增材制造合金钢硬度及抗拉强度的定量评价与表征。     

Investigations on the mechanical properties and microstructure of dissimilar cp-titanium and AISI 316L austenitic stainless steel continuous friction welds

Friction welding process is a solid state joining process that produces a weld under the compressive force contact of one rotating and one stationary work piece. In this study, the friction welding of dissimilar joints of AISI 316L stainless steel and cp-titanium is considered. The optical, scanning electron microscopy studies of the weld were carried out. Moreover, the X-ray diffraction analysis was performed. The integrity of welds was achieved by the micro hardness and tensile tests. The fracture surface was examined by the scanning electron microscopy. The study showed that the magnitude of tensile strength of the dissimilar welded specimen was below that of the titanium base material if preheating was not applied at the interface. The high weld tensile strength was achieved by preheating the 316L stainless steel material to 700 °C, smoothing and cleaning of the contact surfaces. Results illustrated that in dissimilar joints, different phases and intermetallic compounds such as FeTi, Fe₂Ti, Fe₂Ti₄O, Cr₂Ti and sigma titanium phase were produced at the interface. The presence of brittle intermetallic compounds at the interface resulted in degradation of mechanical strength which in turn led to premature failure of joint interface in the service condition. Preheating caused to produce oxide layer at the interface which was harmful for bonding. The oxide layer could be eliminated by applying pressure and smoothing the surface. Results of hardness tests illustrated that the high hardness was occurred in the titanium side adjacent to the joint interface. Moreover, the optimum operational parameters were obtained in order to achieve the weld tensile strength greater than the weak titanium material.     

The influence of post‐heat treatments on the tensile strength and surface hardness of selectively laser‐melted AlSi10Mg

To improve the mechanical properties of cast aluminium alloys several post‐heat treatments are known. However, these treatments cannot directly be transposed to additively via selective laser melting manufactured aluminium alloys, e. g., aluminium‐silicon‐magnesium (AlSi10Mg). Therefore, this study aims to determine suitable post‐heat treatments to optimise the mechanical properties of SLM‐built AlSi10Mg specimen. The influence of various post‐heat treatment conditions on the material characteristics was examined through hardness and tensile tests. The findings indicate that the Vickers hardness and ultimate tensile strength could not be improved via secondary precipitation hardening, whereas the fracture elongation shows a value which is distinctly higher than the values of a comparable cast alloy. Solution annealing at 525 °C reduces the hardness and the ultimate tensile strength by about 40 % and increases the fracture elongation three times. A subsequent precipitation hardening allows recovery of 80 % of the as‐built hardness, and 90 % of the previous ultimate tensile strength combined with maintaining an improved fracture elongation of about 35 % compared to the respective as‐fabricated condition.     

High temperature tensile properties of 316LN stainless steel investigated using automated ball indentation technique

Type 316LN stainless steel (SS) is the principal structural material for the components of sodium cooled fast reactors operating under elevated temperature conditions. In order to assess the degradation in strength of service exposed components using a small specimen testing technique such as automated ball indentation (ABI), it is necessary to carry out prior detailed ABI studies on the virgin material. In this investigation, the tensile behaviour of as-received 316LN SS were investigated at several temperatures in the range 298–973 K using ABI technique. The load-depth of indentation data measured from ABI tests was analyzed using semi-empirical relationships to obtain the tensile properties. The yield stress and the flow curves were determined by correlating ABI results with corresponding uniaxial tensile test results. Trend curve for tensile strength with temperature, as estimated from ABI tests, exhibited a plateau region in the temperature around 823 K, similar to uniaxial tensile tests. The variations of strength coefficient, strain hardening exponent, yield ratio, hardness and uniform ductility with temperature were evaluated from ABI tests. The ABI technique was found to estimate the influence of temperature on tensile properties sensitively.     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Austempering heat treatments of ductile iron using molten metal baths

This work aims to evaluate the use of two different zinc–tin and zinc–aluminum molten metal baths on austempering heat treatments performed in ductile cast iron. Samples were extracted from as-cast standard Y-blocks for austempering heat treatments. The samples were heated for austenitization at 910°C for 90?min and further cooled in two different molten metal baths for austempering: zinc–tin and zinc–aluminum alloys at 370 and 400°C, respectively, for 30, 60 and 90?min. The Zn–50?wt% Sn hypoeutectic alloy and the Zn–5?wt% Al eutectic alloy were chosen for the molten metal baths. After heat treatments, the samples were analyzed by optical and scanning electron microscopy, Brinell hardness, Vickers microhardness, Charpy impact and tensile tests, and fracture mode analysis. The results indicated the viability of using Zn–Al and Zn–Sn molten metal baths as a substitute of molten salts. When the austempering temperature was increased from 370 to 400°C, the hardness, tensile strength, and elongation decreased, while impact energy increased. The ideal processing parameters were obtained for austempering at 370°C for 60?min, where the austempered ductile cast iron presented a microstructure completely formed by finer ausferrite.     

等温处理时间对触变挤压锡青铜轴套的组织和性能的影响

采用冷轧-等温处理SIMA法(CRITSIMA法)制备半固态锡青铜坯料并将其挤压成锡青铜轴套,研究了等温处理时间对其微观组织和力学性能的影响。结果表明：随着等温处理时间的延长锡青铜轴套的平均晶粒尺寸随之增大,晶粒的粗化速率为296μm³/s,形状因子先增大后减小,布氏硬度和延伸率先提高后降低,抗拉强度逐渐降低。在910℃等温15 min的锡青铜轴套其综合性能最高,形状因子为0.74,平均晶粒尺寸为63.56μm,抗拉强度为368 MPa,延伸率为4.5%,布氏硬度为126 HBW。     

15CrMo钢的高温时效性能的变化规律及计算模型

根据现有标准DL/T 787-2001提供的数据分析了随温度和球化等级的改变,15CrMo钢的碳化物相中钼元素含量、抗拉强度、屈服强度、伸长率、断面收缩率以及硬度的变化规律,同时建立了相关计算模型,并且预测出球化等级为1.5,2.5,3.5和4.5级所对应的性能参数值.此外还分别给出了依据常温抗拉强度、屈服强度、布氏硬...     

Hot tensile and fatigue behaviour of zinc–aluminum alloys produced by gravity and squeeze casting

The tensile and fatigue properties of zinc–aluminum alloys (ZA-8, ZA-12 and ZA-27) in squeeze and gravity cast forms have been investigated. Tensile tests were conducted at ambient and elevated temperatures up to 150 °C. At low temperatures, the ultimate tensile strength and yielding strength of the squeeze cast alloys have been found to be superior those of the gravity-cast alloys, as the temperature increased they decreased. In the same way, Brinell hardness of the squeeze cast alloys were obtained at higher values than gravity castings. The fatigue tests were performed at a constant speed of 400 rev/min and under a number of stress levels ranging from 100 to 150 MPa. The fatigue behaviour results of the ZA alloys were similar to obtained from the tensile testing. The squeeze cast alloys exhibited good fatigue resistance in proportion to the gravity castings. Metallography examinations showed that the microstructure of the castings differed according to the method of casting used. It was considered that the mechanical properties of the alloys were affected from these micro-structural changes.     

长管拖车气瓶鼓包失效分析

采用化学成分分析、室温拉伸试验、低温冲击试验、布氏硬度试验以及金相检验等方法分析了某长管拖车气瓶产生鼓包的原因。结果表明:气瓶鼓包是由于热处理不当,导致显微组织异常,出现较多铁素体,降低了气瓶的强度和硬度;当气瓶局部工作压力超过其屈服强度时,便会产生鼓包现象。     

Influence of the impact sintering temperature on the structure and properties of samples from the different iron powders

The studies of the consolidation, structure and mechanical properties of samples from two types of iron powder are carried out. The coarse and less pure PZH3M2 as well as fine and purer DIAFE5000 powders were used. The samples are obtained by means of impact sintering method in the temperatures range of 500–1100 °C. The impact energy was 1200 J/cm³, and the initial deformation velocity - 6.5 m/s. Samples are obtained in the form of disks with a diameter of 25–27 mm and 9–10 mm high. For carrying out different mechanical tests the bars were cut out from disks. The tensile, compression, three-point bend of notched samples tests were carried out, as well as the Brinell hardness was measured after the corresponding processing of the bars. The characteristics of strength and plasticity of samples depending on the impact sintering temperature are determined. The polished surface of different samples and the fracture surface are investigated. It is established that the high density of samples is reached at a temperature of 600 and 700 °C respectively for fine and coarse powders. The samples obtained at these impact sintering temperatures possess rather low electrical resistivity, high strength, hardness, but the lowered plasticity. Namely, the samples from the PZH3M2 and DIAFE5000 powders sintered at the temperature of 700 °C have respectively: ultimate tensile strength - 406 and 336 MPa, yield stress - 353 and 190 MPa, contraction ratio - 26 and 78%, limit stress (at the fracture) - 501 and 933 MPa, the maximum crack tip stress – 738 and 876 MPa, the fracture energy at a bend of the notched samples - 4.8 and 51.2 J/cm³ and also Brinell hardness - 1467 and 847 MPa. The increase of the samples impact sintering temperature leads to grain growth, decrease of the samples strength and increase of their plasticity. At the same time the structure of samples from the DIAFE5000 powder is more fine-grained than at samples from the PZH3M2 powder.     

Relationship between composition,structure, and mechanical properties of a condensed composite of copper–tungsten system

For a copper–tungsten microlayered composite material for electrical contact applications, which is prepared by electron-beam evaporation-condensation, the changes in its structure, conductivity, hardness, and mechanical properties in tension at room temperature and elevated temperatures are studied versus the tungsten content and heat treatment conditions. New morphological features of the condensed composite and the related changes in the material properties have been revealed. The conditions for the formation of structural defects and their influence on mechanical properties and fracture behavior of the material in tensile tests have been investigated. A relationship has been established between the tungsten content of the composite, its structure, strength, and hardness.     

Influence of pre-strain on the wear resistance of a plain carbon steel

Dry sliding wear behaviour of a plain carbon steel in different pre-strained conditions was examined in the severe wear regime using a pin-on-disk wear testing machine. The severe wear regime was ascertained by determining wear rates of the unstrained material at different loads. The primary experiments were supplemented by microstructural characterization, hardness assessment of specimens before and after wear tests, determination of tensile properties of the pre-strained specimens and SEM examination of the worn-out surfaces and subsurfaces. The results indicate that the wear rate of the specimens first increases up to 15% pre-strain and then decreases, while the hardness and tensile strength of the specimens monotonically increases with increased pre-strain. The mechanism of wear is observed to be subsurface cracking and delamination aided by oxidative wear. The imposed pre-strain on a specimen is considered to aggravate the nucleation of voids and microcracks resulting in degradation of wear resistance of the pre-strained specimens. The results infer that wear rates of pre-strained materials are governed by ductility or toughness apart from hardness and strength.     

Effect of welding parameters on microstructure and mechanical properties of friction stir spot welded 5052 aluminum alloy

Friction stir spot welding (FSSW) is a newly-developed solid state joining technology. In this study, two types of FSSW, normal FSSW and walking FSSW, are applied to join the 5052-H112 aluminum alloy sheets with 1 mm thickness and then the effect of the rotational speed and dwell time on microstructure and mechanical properties is discussed. The lower sheet material underneath the hook didn’t flow into the upper sheet due to the concave surface in the shoulder and groove in the anvil. The hardness profile of the welds exhibited a W-shaped appearance and the minimum hardness was measured in the HAZ. The results of tensile/shear tests and cross-tension tests indicate that the joint strength decreases with increasing rotational speed, while it’s not affected significantly by dwell time. At the rotational speed of 1541 rpm, the tensile/shear strength and cross-tension strength reached the maximum of 2847.7 N and 902.1 N corresponding to the dwell time of 5 s and 15 s. Two different fracture modes were observed under both tensile/shear and cross-tension loadings: shear fracture and tensile/shear mixed fracture under tensile/shear loadings, and nugget debonding and pull-out under cross-tension loadings. The performance of the welds plays a predominant role in determining the type of fracture modes. In addition, the adoption of walking FSSW brings unremarkable improvements in weld strength.     

Fracture toughness behaviour of a magnesium alloy metal-matrix composite produced by the infiltration technique

Metal-matrix composites comprising short δ-alumina fibres embedded in an Mg 10Al0.4Zn alloy were produced by the squeeze infiltration process, with a fibre volume fraction of 20%. Tensile, hardness and fracture toughness tests were performed at room temperature on both the alloy matrix and the composite in the as-cast as well as in the T6 heat-treated condition. In the as-cast condition it was found that the composite had a markedly increased stiffness, tensile strength and hardness but slightly lower ductility and fracture toughness than the alloy matrix. Whilst a T6 heat treatment improved the mechanical properties of the magnesium alloy matrix, it adversely affected the tensile properties and fracture toughness of the composite.