Warm compacted NbC particulate reinforced iron-base composite(Ⅱ)--Microstructure and properties

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｂｉｇｇｅｓｔｐｒｏｂｌｅｍｓｉｎｔｈｅｆａｂｒｉｃａｔｉｏｎｏｆｐａｒｔｉｃ ｕｌａｔｅｒｅｉｎｆｏｒｃｅｄｍｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓ (ＭＭＣｓ)ａｒｅｔｈｅｅｖｅｎｄｉｓｔｒｉｂｕｔｉｏｎｓｏｆｒｅｉｎｆ     

NbC增强Fe-Cr-C耐磨堆焊合金组织与磨粒磨损性能

以H08A为焊芯,在Fe-Cr-C耐磨合金焊条药皮中加入NbC,对堆焊层组织及NbC对堆焊层硬度和耐磨性的影响进行了研究.结果表明,NbC增强Fe-Cr-C耐磨合金的宏观硬度和耐磨性都高于Fe-Cr-C合金,宏观硬度达到61.6 HRC,比Fe-Cr-C耐磨合金提高9.6%;相对耐磨性提高60%.NbC增强Fe-Cr-C耐磨合金中NbC硬质相断面呈不规则形状,分布于M7C3之间,或镶嵌在M7C3中,以菱形或多边形居多,NbC分布不均匀,有局部聚集的区域.与Fe-Cr-C耐磨合金的共晶碳化物比较,Fe-Cr-C-NbC合金的共晶碳化物要粗大,共晶碳化物的间距也较大.     

Warm compacted NbC particulate reinforced iron-base composite(Ⅰ)--Effect of fabrication parameters

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓ (ＭＭＣｓ)ｃｏｍｂｉｎｅｓｔｈｅａｄｖａｎｔａｇｅｓｏｆｄｉｆｆｅｒｅｎｔｍａｔｅｒｉａｌｓ.Ｉｔｉｓａｈｏｔｓｐｏｔｉｎｔｈｅｐａｓｔｄｅｃａｄｅｓ .Ｐｏｗｄｅｒｍｅｔａｌｌｕｒｇｙ (     

TiC-NbC超硬质相耐磨堆焊焊条的研究

本文采用廉价钛铁、铌铁和含碳材料等．以焊条药皮合金化，通过电弧冶金反应，获得含TiC、NbC超硬质相的堆焊层。极大地提高了堆焊层的耐磨性。研制出含TiC－NbC新型耐磨合金堆焊条。具有广泛地应用前途。     

机械合金化制备金属铌的难熔化合物

金属难熔化合物材料因其具有良好的高温热稳定性能和力学性能，而呈现出广阔的应用前景。本文借助于机械合金化技术成功地制备出铌的难熔化合物ＮｂＣ、ＮｂＢ，并对其合成过程进行了分析。     

APT analysis of WC-Co based cemented carbides

A method for quickly producing sharp and site-specific atom probe specimens from WC-Co based cemented carbides was developed using a combination of electropolishing, controlled back-polishing and FIB milling. Also, a method for measuring the amount of segregated atoms to an interface between two phases with a big difference in field needed for field evaporation was developed. Using atom probe tomography, the interface chemistry of WC/WC grain boundaries, WC/(M,W)C phase boundaries and WC/binder phase boundaries was analysed. In addition, the transition metal solubility in WC was determined.     

Multiscale modelling approach for predicting solidification structure evolution in vacuum arc remelted superalloy ingots

Abstract

The present paper describes the mathematical development and validation of a comprehensive stochastic model capable of predicting at the mesoscopic level the solidification structure, Laves, and NbC phases in superalloy ingots processed by vacuum arc remelting (VAR) technology. The multiscale modelling approach consists of a coupling between a fully transient deterministic macroscopic code and a stochastic mesoscopic solidification structure code. Predictions from the model were validated against experimental measurements. Multiscale model predictions are compared against a commercial size VAR ingot.     

Effect of Nb on long-term creep life of JIS SUS304HTB and JIS SUS347HTB steels – heat-to-heat variation and life assessment of stainless steels

Heat-to-heat variation in creep life has been investigated for the 9 heats of JIS SUS 304HTB (18Cr–8Ni steel) and also for the 9 heats of JIS SUS 347HTB (18Cr–12Ni–Nb steel) in the NIMS Creep Data Sheets, mainly taking the effect of Nb into account. The heat-to-heat variation in creep life of 304HTB is mainly caused by the variation in precipitation hardening due to fine NbC carbides at short times, while it is mainly caused by the variation in available nitrogen concentration, defined as the concentration of nitrogen free from AlN and TiN, at long times. The heat-to-heat variation in creep life of 347HTB is mainly explained by the variation of boron concentration, 3–27 ppm, but not by the variation of solution temperature, Nb/C atomic ratio and phosphorus concentration. Boron reduces the coarsening rate of fine M₂₃C₆ carbides along grain boundaries, which enhances the grain boundary precipitation hardening.     

Effects of Nb on stress corrosion cracking of high-strength low-alloy steel in simulated seawater

In this study, simulated heat-affected zone (HAZ) of Nb-free and Nb-bearing steel were obtained, and SEM, TEM, and slow strain rate tensile (SSRT) tests were performed to investigate the effect of Nb on the stress corrosion cracking (SCC) behavior of high-strength low-alloy (HLSA) steel in simulated seawater with or without hydrogen charging. The addition of Nb significantly refined the grains and uniformed the microstructure of HLSA. Nb hardly affected the SCC susceptibility of BM and HAZ without hydrogen-charging. However, after charging with 10 mA cm⁻², the SCC resistance of Nb-bearing steel, especially the coarse grain HAZ (CGHAZ) improved drastically, and the process of crack initiation and propagation was inhibited owing to the hydrogen trap function of NbC precipitates.     

Preparation and high temperature performance of NbC layer in TRISO particles

TRISO particles with new coating layers was designed to adapt higher temperature. In this work, NbC coating layers were prepared by a novel two-step method: The original NbC coating layer was prepared from NbCl₅ and C₃H₆ by chemical vapor deposition method. The flow rate of the C₃H₆ should be relatively low to avoid the C impurity. The NbC layer was then heated with carbon powders at high temperature. Since the C atoms can diffuse into the NbC coating layer and react with Nb₂C at high temperature. The Nb₂C impurity comes from the deposition was removed after the thermal treatment. The crystal of NbC layer grow up and has a change of preferred orientation at high temperature. The heat treatment has slight effect on the hardness of the pure NbC layer. Our result shows the NbC coating layer has good adaptability to the high temperature environment in VHTR.