Combining indentation and diffusion couple techniques for combinatorial discovery of high temperature shape memory alloys

We demonstrate the possibility of accelerated identification of potential compositions for high-temperature shape memory alloys (SMAs) through a combinatorial material synthesis and analysis approach, wherein we employ the combination of diffusion couple and indentation techniques. The former was utilized to generate smooth and compositionally graded inter-diffusion zones (IDZs) in the Ni–Ti–Pd ternary alloy system of varying IDZ thickness, depending on the annealing time at high temperature. The IDZs thus produced were then impressed with an indenter with a spherical tip so as to inscribe a predetermined indentation strain. Subsequent annealing of the indented samples at various elevated temperatures, T_a, ranging between 150 and 550 °C allows for partial to full relaxation of the strain imposed due to the shape memory effect. If T_a is above the austenite finish temperature, A_f, the relaxation will be complete. By measuring the depth recovery, which serves as a proxy for the shape recovery characteristic of the SMA, a three-dimensional map in the recovery–temperature–composition space is constructed. A comparison of the published A_f data for different compositions with the T_a data shows good agreement when the depth recovery is between 70% and 80%, indicating that the methodology proposed in this paper can be utilized for the identification of promising compositions. Advantages and further possibilities of this methodology are discussed.     

Near-threshold propagation of mode II and mode III fatigue cracks in ferrite and austenite

The near-threshold behavior of mode II and mode III long fatigue cracks in ferritic (ARMCO iron) and austenitic (X5CrNi18-10) steel were experimentally studied using various samples specially prepared to obtain the effective threshold values ΔK_IIeff,th and ΔK_IIIeff,th. In both investigated materials, the effective thresholds for mode III were ～1.7 times higher than those for mode II. Three-dimensional topological data obtained by the examination of fracture surfaces using stereophotogrammetry were utilized to identify crack growth micromechanisms. In austenite, mode I branching of both the mode II and mode III cracks started at the very onset of crack growth. On the other hand, all cracks in ferrite propagated in crystallographically assisted local mixed mode I + II + III with mode II dominance. These experimental results can be understood in terms of crack growth micromechanisms according to a deformation model in ferrite and a decohesion model in austenite. The dissimilarity of growth mechanisms in ferrite and austenite may be attributed to a different number of available slip systems in body-centered cubic and face-centered cubic metals.     

Development of a white cast iron of fracture toughness 40 MPa√m

White cast irons are limited by their brittleness, and improvement of toughness has proved an elusive goal. In this study a variety of strategies have been applied in combination to achieve improved toughness. Eutectic carbide volume fraction is reduced and non-standard heat treatments are applied.

The fracture toughness of the experimental low-carbon white cast iron is found to be superior to that of a conventional 20Cr—2Mo—1Cu white iron for most heat-treated conditions. A maximum toughness of 40 MPa√m was achieved in the experimental white iron, using a four hour high-temperature treatment at 1125°C. This value is substantially higher than anything previously reported for a white cast iron, of any carbon content.

A field trial of grinding mill liners manufactured in the experimental white iron was carried out and indicated service lives of more than 80% longer than those obtained with the currently used pearlitic steel.     

Influence of Ti/N ratio on simulated CGHAZ microstructure and toughness in X70 steels

Abstract

Three API 5L X70 steels with different Ti and N contents and otherwise identical chemistry were selected to investigate the effect of Ti/N ratio on the toughness in coarse grained heat affected zone (CGHAZ). A Gleeble 3500 thermomechanical simulator was used to simulate the thermal profile of CGHAZ of double submerged arc welding process. The microstructure was examined by optical microscopy. Statistics of CGHAZ grain coarsening were compiled by measuring the prior austenite grain size. Toughness of the simulated CGHAZ regions was evaluated by Charpy V-notch testing at ?20 and ?40°C. Morphology of the impact fracture surface was investigated using SEM. Steel B with Ti/N ratio of 3·22 (slightly below stoichiometric) showed slightly higher toughness in the simulated CGHAZ due to higher volume fraction of austenite grains less than 80 μm in diameter.     

NY—102型便携式超声波成象仪

本文将计算机技术，信号处理技术与超声检测技术结合起来，研制成功ＮＹ－１０２型便携式超声波成象仪，该仪器具有普通超声波探伤仪的全部功能，而且可以在屏幕上显示缺陷形状及尺寸大小，并能将缺陷图象存档和打印输出，经燕山石化现场试验表明，该仪器具有缺陷分辨率高，定位精确，图象清晰，操作简便等优点，在石化，压力容器等领域有着广泛的应用前景。     

高镍合金铸铁的组织与性能研究

采用高频感应加热设备熔配合Ni量为20％～60％的高镍合金铸铁样品,研究了Ni含量对铸铁基体组织、石墨形态及合金硬度的影响.结果表明,在高Ni合金铸铁中,随着Ni含量的增大,一方面,合金的石墨化能力显著增强,可以获得无渗碳体相的凝固组织,石墨形态由粗大片状依次向细小片状→点状→粗化点状转变;另一方面,合金结晶温度区间变窄,成分过冷倾向减小,奥氏体枝晶分枝能力减弱,形成了形态不甚发达的粗大枝晶乃至等轴晶组织,在Ni余量为20％及以上时高镍合金铸铁的硬度呈现出单调减小的趋势.     

奥氏体不锈钢对接焊接接头超声波检测对比试块的制作

奥氏体不锈钢对接焊接接头的超声检测中,带焊缝的对比试块的制作对检测评价结果非常重要,也能为超声波仪器探头系统的灵敏度调整提供较为客观有效的参考。为使对比试块更贴近实际检测的需要,采用将试块竖立焊接方式设计制作了超声检测对比试块。并与平躺x型坡口对比试块进行了细致对比,结果显示采用竖立焊接试块调试的检测灵敏度更为恰当。实际检测工作也验证了竖立焊接对比试块能更好地满足检测要求。     

冷作模具钢SDC55的Q-P-T性能和微观组织研究

主要研究和探索了对新型冷作模具钢SDC55处理的Q-P-T工艺及其微观组织,测试了不同Q-P-T工艺下SDC55试样的硬度、冲击韧性以及残余奥氏体的含量和稳定性,用TEM观察Q-P-T处理后试样的微观组织。实验结果表明,SDC55的优化工艺为930℃奥氏体化,290℃PT温度时间2 min,最后经过180℃一次2 h回火。与常规的淬、回火工艺(930℃奥氏体化淬火,180℃回火两次,每次2 h)相比较,经过Q-P-T处理之后,SDC55的韧性从123 J提高到131 J,硬度保持不变,均为60 HRC。对微观组织和残余奥氏体分析发现,经Q-P-T处理后SDC55的残余奥氏体稳定性得到提高,从而使材料的冲击韧性提高。     

Austenite particle coarsening and delta-ferrite grain growth in model Fe–Al alloy

Abstract

The grain growth kinetics of delta-ferrite was investigated in a model Fe–Al alloy in which a small volume fraction of austenite particles is used to control grain growth. The specimens were heated to different temperatures in the two phase (delta-ferrite+austenite) region and held for times between 5 min and 288 h followed by water quenching. The coarsening kinetics of the austenite particles could be described both in terms of bulk (t^1/3) and grain boundary (t^1/4) diffusion. The growth of the delta-ferrite grains was dominated by the pinning effect of the austenite particles. When the particle pinning pressure was much larger than the driving force for grain growth, the growth of delta-ferrite grains was completely pinned. Under conditions in which the particle pinning force and the driving force for grain growth were comparable, ferrite grain growth occurred at a rate which is proportional to the rate of coarsening of the austenite particles. When the particle pinning force is smaller than the driving force, grain growth occurs at a rate which is lower than that expected without pinning.

On a examiné la cinétique de croissance de grain de ferrite delta dans un alliage modèle de Fe-Al dans lequel une petite fraction volumique de particules d’austénite est utilisée pour contrôler la croissance de grain. On a chauffé les échantillons à différentes températures dans la région à deux phases (ferrite delta + austénite) et on les a maintenus pour des durées allant de 5 minutes à 288 heures, puis on les a trempés à l’eau. On pourrait décrire la cinétique de grossissement des particules d’austénite tant en fonction de la diffusion volumique (t^1/3) que de la diffusion aux joints de grain (t^1/4). La croissance des grains de ferrite delta était dominée par l’effet d’épinglage des particules d’austénite. Lorsque la pression d’épinglage de particule était beaucoup plus grande que la force motrice pour la croissance de grain, la croissance des grains de ferrite delta était entièrement épinglée. Dans les conditions où la force d’épinglage de particule et la force motrice pour la croissance de grain étaient comparables, la croissance de grain de ferrite se produisait à une vitesse proportionnelle à la vitesse de grossissement des particules d’austénite. Lorsque la force d’épinglage de particule était plus petite que la force motrice, la croissance de grain se produisait à une vitesse plus faible que la vitesse sans épinglage.     

超低碳Cr26－Ni28－Mo5－Cu3－Nb0．35铸造不锈钢的组织和耐蚀性能

用金相、透射电子显微镜、电子探针与扫描电镜分析研究得出，超低碳Ｃｒ２６－Ｎｉ２８－Ｍｏ５－Ｃｕ３－Ｎｂ０．３５不锈钢铸态组织中含有σ相，经８５０～１１２０℃热处理均可形成σ相，包括（Ｆｅ－Ｃｒ）σ相，（Ｆｅ－Ｍｏ）σ相和（Ｃｒ－Ｎｉ－Ｓｉ）σ相；８５０℃左右有Ｍ６Ｃ型碳化物和ＮｂＣ析出。该钢经１１５０℃２ｈ水冷固溶处理后，具有优良的耐腐蚀性能。