The phosphorus effect on the superplastic deformation of NiAl

The P effect on the superplastic deformation of NiAl has been investigated. It is shown that P segregates to grain boundaries and the segregation has profound influence on the high temperature tensile properties of the NiAl alloy. The segregation retards dynamic recovery and recrystallization that leads to a decrease in elongation and enhancement in cavitation compared with the stoichiometric NiAl. Therefore, the P has harmful effect on the superplastic deformation of NiAl.     

Comparative study on NiAl and FeAl intermetallic-bonded diamond tools and grinding performance for Si3N4 ceramic

Metal-bonded diamond tools are widely used for machining hard and brittle materials such as ceramic and stone. The metal bonds are normally based on alloys composed of Fe, Co, Ni, Cu, Sn, Zn, or Cr. However, high heavy metal concentrations are hazardous to the environment and tool operators. Furthermore, the high density of these metal bonds results in excessively heavy tools, requiring high energy and intensive labor during operation. Therefore, we propose two environmentally friendly and lightweight metal bonds based on NiAl and FeAl intermetallics for diamond tools by reactive hot-press sintering. The effect of sintering temperature on the microstructure and mechanical properties of NiAl and FeAl was examined and the tribological behavior of NiAl and FeAl on Si₃N₄ ceramic balls was investigated. Grinding performance of the sintered diamond tools on Si₃N₄ ceramic was also compared. Our results reveal that B2-ordered NiAl and FeAl are obtained at sintering temperatures in the range of 700–1100 °C. The relative density of sintered NiAl is higher than that of FeAl, while the Vickers hardness and flexural strength of NiAl are lower than that of FeAl. Compared with FeAl, NiAl demonstrates higher wear resistance in a friction test against Si₃N₄ ceramic, while FeAl-bonded diamond tools demonstrate a higher grinding ratio than NiAl-bonded diamond tools due to enhanced self-sharpening ability. Nevertheless, diamond tools based on both NiAl and FeAl can be used to grind Si₃N₄ ceramics.     

定向凝固NiAl-28Cr-5.8Mo-0.2Hf合金的高温拉伸蠕变行为

研究了定向凝固NiAl-28Cr-5.8Mo-0.2Hf合金的显微组织和在982－1100℃,50-124MPa应力下的高温蠕变行为，该合金是由NiAl相。Cr(Mo)相和少量Hf的固溶体相组成。蠕变测试结果表明：蠕变曲线是由较短的减速蠕变阶段和较长的加速蠕变阶段组成，且蠕变后的显微组织变化不大，蠕变变形机制是由位错攀移机制所控制。加强蠕变阶段蠕变速率的增加是由于裂纹的形成与扩展引起的。     

Interfacial Segregation, Pore Formation, and Scale Adhesion on NiAl Alloys

Ni-40 and 50at various times in oxygen. Auger electron microscopy was used to study the interface chemistry after scale spallation in ultra high vacuum. The interfacial failure stresses were determined using a tensile pull tester and related to the interface chemistry, pore area and density. Results showed that sulfur started to segregate to areas of the Al²O³/Ni40Al interface, where the scale was in contact with the alloy after a complete layer of -Al²O³ developed there; the concentration then gradually increased to a steady level of ~0. 2 at %. However, sulphur did not segregate to similar areas of the Al²O³/Ni50Al interface even after extended oxidation when it was amply present on interfacial void faces. This behavior demonstrated a strong dependence of interface segregation on NiAl alloy composition. Interfacial failure stress was found to decrease with increasing sulfur content between voids and with higher interface porosity. The level of porosity was strongly related to the sulfur content in the alloy. When Ni40Al was doped with excess sulfur, the segregation behavior did not change, but the interfacial pore density increased significantly. The detrimental effect of sulfur on scale adhesion is 2-fold: to weaken the interface and to enhance interfacial pore formation.     

热处理温度对新型马氏体时效不锈钢微观组织和性能的影响

针对一种以Al作为主要强化元素的新型马氏体时效不锈钢,通过力学性能测试、光学显微镜观察和透射电子显微分析方法,研究不同的热处理温度对实验钢力学性能和微观组织的影响。结果表明:该实验钢的抗拉强度最高可达1876MPa,屈服强度可达1762MPa,具有良好的强韧性配合。固溶处理后形成了具有高密度位错的细小板条马氏体组织,在时效过程中,马氏体基体上弥散析出的NiAl相使其强度得到大幅度的提升。随着时效温度的提高,NiAl析出相颗粒逐渐长大粗化,从而使强度在到达峰值后迅速下降,出现了过时效现象。实验钢经过820℃固溶+(-70℃)冷处理+540℃时效处理后可获得良好的综合力学性能。     

High Temperature Materials Based on the Intermetallic Compound NiAl Reinforced by Refractory Metals for Advanced Energy Conversion Technologies

Advanced NiAl‐based high temperature materials are developed and characterized for structural applications in energy conversion systems. The intermetallic compound NiAl with B2 superlattice structure exhibits superior physical and high temperature mechanical properties, and excellent oxidation resistance. Disadvantages of polycrystalline pure NiAl are the lack in plasticity and fracture toughness at room temperature and insufficient high temperature strength at temperatures above 800 °C. The refractory metals Cr, Mo, and Re form with NiAl quasi‐binary eutectic systems which enable to produce metal fibres reinforced NiAl‐based alloys in the as‐cast condition and by performing directional solidification. These in‐situ composites show fine‐grained and thermally stable microstructures possessing high temperature strength, superior creep resistance and sufficient room temperature ductility.     

EFFECT OF IRON ON FORMATION OF MECHANICALLY ALLOYED NiAl ALLOY AND ITS MECHANICAL PROPERTIES

ＥＦＦＥＣＴＯＦＩＲＯＮＯＮＦＯＲＭＡＴＩＯＮＯＦＭＥＣＨＡＮＩＣＡＬＬＹＡＬＬＯＹＥＤＮｉＡｌＡＬＬＯＹＡＮＤＩＴＳＭＥＣＨＡＮＩＣＡＬＰＲＯＰＥＲＴＩＥＳＪ．Ｔ．Ｇｕｏ;Ｌ．Ｚ．Ｚｈｏｕ;Ｚ．Ｇ．ＬｉｕａｎｄＷ．Ｍ．Ｙｉｎ（Ｉｎｓｔｉｔｎｔｅｏｆ...     

二元NiAl金属间化合物单晶的制备

在小型定向凝固装置上,采用两次方向相反的定向凝固工艺,成功地制备出生长分别为１５,３０及６０ｍｍ／ｎ的Ｎｉ５２Ａｌ４８单晶。     

NiAl基多相金属间化合物的显微组织,超塑性研究

本文研究了金属间化合物Ni—25Al—25Cr的显微组织和超塑性及其变形机理.该合金的显微组织由NiAl则基体和α-Cr,β-Ni（Al,Cr）;γ'-Ni3（Al,Cr）的三元共晶体组成,在NiAl基体中还均匀分布着大量弥散的α-Cr沉淀相在1123—1223K之间以22×10-43．3×10－2S－1的应变速率拉伸变形时．该合金表现出高达480％的超塑性超塑性变形的断裂主要是由于晶界滑移和晶粒转动所产生的空洞和晶内解理所致.本文还对超塑性变形的机理进行了初步讨论.     

原位内生多相复合材料（NiAl—28Cr—6Mo）—TiC的高温力学行为

运用燃烧合成了工艺制备了一种多相内生金属间化合物基复合材料（ＮｉＡｌ－２８Ｃｒ－６Ｍｏ）－ＴｉＣ复合材料的高温变形行为显示流变应力随温度升高或初始应变速率减小而降低,服从幂指数规律,求出了不同含量ＴｉＣ时复合材料的应务指数ｎ和激活能Ｑ,与同类ＮｉＡｌ基复合材料进行了比较分析。