等离子熔覆含亚微米碳化铌铁基耐磨合金组织与性能的研究

采用等离子熔覆(PTA)在Q235钢上制备含亚微米碳化铌Fe-Cr-B-C-Nb熔覆层,通过改变合金成分,分别设计含超细碳化铌、含共晶硼化物、含超细碳化铌+共晶硼化物、含超细碳化铌+初生Fe2B硬质相的熔覆层,研究不同尺寸硬质相对Fe-Cr-B-C-Nb熔覆层组织与性能的影响,并与市售常用Fe-Cr-C耐磨材料对比。结果表明:细小硬质相有助于改善合金冲击变形能力,含亚微米碳化铌和共晶硼化物的合金具有优良的综合性能,耐磨性为Fe-Cr-C耐磨材料的4倍多,且冲击变形能力优于Fe-Cr-C耐磨材料。     

Creep resistance of Fe–Ni–Cr heat resistant alloys for reformer tube applications

Relations between microstructure, phase transformations and creep resistance of austenitic Fe–Ni–Cr alloys are investigated. As-cast alloys with different silicon contents and an ex-service tube are submitted to laboratory agings to trigger specific phase transformations, and subsequently creep-tested at 950°C under stresses of 24–48?MPa. As-cast microstructures contain interdendritic chromium-rich M₇C₃ carbides with niobium-rich MC carbides. After aging at 950°C, primary M₇C₃ carbides transform into chromium-rich M₂₃C₆ carbides, associated to a loss in creep strength. The G phase present in the ex-service alloy is reversed into MC carbides by a heat treatment at 1100°C, associated to a slight decrease in creep resistance. Besides, the addition of silicon is highly detrimental to creep strength. Results can be used for alloy design.     

Sintering of alumina-niobium carbide composite

Several studies have been focused on particulate-dispersed Al₂O₃ composites in order to improve both room and high temperature mechanical properties and wear resistance. In the present work Al₂O₃-NbC composites have been pressureless sintered and their microstructures analysed as a function of NbC and Y₂O₃ concentration, the latter added as sintering aid. The compositions used in this study were Al₂O₃-xNbC and (Al₂O₃ 3%Y₂O₃)-xNbC, (x = 10, 20 and 40 wt%) and the sintering was performed at 1650 °C/30 min and 1750 °C/15 min. A density greater than 96% of the theoretical density was reached even for those materials sintered at 1650 °C. The observed microstructure was more homogeneous for the samples with Y₂O₃ addition and the Y₃Al₅O₁₂ phase was detected. The Al₂O₃ grain growth restraining due to the NbC concentration was more pronouncedly in samples sintered at 1750 °C.     

激光熔覆Ni3Si基复合涂层相、组织及高温抗氧化性能研究

采用激光熔覆技术在镍基高温合金GH864表面制备了原位合成碳化物TiC、NbC陶瓷颗粒增强Ni3Si金属间化合物基复合涂层，采用XRD、SEM和EDAX等方法，对熔覆层相、组织进行了表征。采用循环氧化法研究了熔覆层在1100℃下的高温抗氧化性能。     

NbC对FeMnSiCrNi合金组织与记忆性能的影响

配制了5种不同Nb，C含量的Fel4Mn5Si9Cr5Ni形状记忆合金，测量了不同温度和不同时间条件下固溶-时效处理的合金记忆性能，采用透射电镜和原子力显微镜观察了合金的显微组织。结果表明NbC的析出对合金的形状记忆性能有明显影响，经1200℃，10h固溶处理后的Fel4Mn5Si9Cr5Ni0．5Nb合金，经800℃，6h时效获得了最好的形状记忆性能，且优于无铌Fel4Mn5Si9Cr5M合金经热机械循环训练的记忆性能指标。显微观察表明经过高温固溶．中温时效处理后的该合金中NbC粒子在合金基体时效析出，有利于合金应力诱发细小马氏体核心的形成。     

5Cr21Mn9Ni4Nb2WN奥氏体耐热钢晶界碳化物对高温塑性的影响

观察了锻造后５Ｃｒ２１Ｍｎ９Ｎｉ４Ｎｂ２ＷＮ钢在８５０°－１２８０℃加热１ｈ水冷固溶处理后，晶界碳化物的类型大小，形貌及其随温度的变化情况。试验证明，１１３０℃以下温度加热时，ＮｂＣ块可作为碳源退化成Ｍ２３Ｃ６颗粒。细粒状和细片状晶界碳化物对提高钢的高温延伸性能和断面收缩性能较为有利，而大尺寸块状和大尺寸薄片状碳化物去弱化了晶界，并对高温塑性产生不利影响。     

Characterization of NbC and (Nb, Ti)N nanoprecipitates in TRIP assisted multiphase steels

Multiphase steels utilising composite strengthening may be further strengthened via grain refinement or precipitation by the addition of microalloying elements. In this study a Nb microalloyed steel comprising martensite, bainite and retained austenite has been studied. By means of transmission electron microscopy (TEM) we have investigated the size distribution and the structural properties of (Nb, Ti)N and NbC precipitates, their occurrence in the various steel phases, and their relationship with the Fe matrix. (Nb, Ti)N precipitates were found in ferrite, martensite, and bainite, while NbC precipitates were found only in ferrite. All NbC precipitates were found to be small (5–20 nm in size) and to have a face centred cubic (fcc) crystal structure with lattice parameter a = 4.36 ± 0.05 Å. In contrast, the (Nb, Ti)N precipitates were found to have a broader size range (5–150 nm) and to have a fcc crystal structure with lattice parameter a = 8.09 ± 0.05 Å. While the NbC precipitates were found to be randomly oriented, the (Nb, Ti)N precipitates have a well-defined Nishiyama–Wasserman orientation relationship with the ferrite matrix. An analysis of the lattice mismatch suggests that the latter precipitates have a high potential for effective strengthening. Density functional theory calculations were performed for various stoichiometries of NbC_x and Nb_xTi_yN_z phases and the comparison with experimental data indicates that both the carbides and nitrides are deficient in C and N content.     

Microstructure and wear resistance of highchromium cast iron containing niobium

In the paper, the effect of niobium addition on the microstructure, mechanical properties and wear resistance of high chromium cast iron has been studied. The results show that the microstructure of the heattreated alloys is composed of M7C3 and M23C6 types primary carbide, eutectic carbide, secondary carbide and a matrix of martensite and retained austenite. NbC particles appear both inside and on the edge of the primary carbides. The hardness of the studied alloys maintains around 66 HRC, not significantly affected by the Nb content within the selected range of 0.48%-0.74%. The impact toughness of the alloys increases with increasing niobium content. The wear resistance of the specimens presents little variation in spite of the increase of Nb content under a light load of 40 N. However, when heavier loads of 70 and 100 N are applied, the wear resistance increases with increasing Nb content.     

原位生成NbC强化Fe-Cr-C堆焊层磨粒磨损性能

在Fe-Cr-C药芯焊丝中添加适量的铌铁粉,通过自动焊制备出含有适量原位生成的硬质相NbC的堆焊层。研究了硬质相NbC的出现对Fe-Cr-C堆焊层组织和性能的影响。结果表明Fe-Cr-C堆焊层中的M_7C_3略大。含有硬质相NbC的堆焊层初生碳化物大小和分布更加均匀,堆焊层硬度达到61.2 HRC,比Fe-Cr-C堆焊层的54.3 HRC提高了约12.71%,相对耐磨性提高49%。硬质相NbC的显微硬度达到2 234 HV。NbC的断面成不规则的多边形,NbC的分布不均匀,成团簇状聚集在一起。     

Y2O3- and NbC-doped ultrafine WC–10Co alloys by low pressure sintering

The nanocomposite WC–10Co powders were prepared through planetary ball milling method. The effects of minor Y₂O₃ and NbC additions on structure, hardness and fracture toughness of ultrafine WC–10Co alloys were investigated using X-ray diffraction, optical microscope, scanning electron microscope and mechanical properties tests. The results show that minor NbC additions refine the WC grains and increase the hardness of the base alloys. The additions of Y₂O₃ decrease the volume fraction of Co₃W₃C phase in ultrafine WC–10Co alloys after low pressure sintering, and thus increase the fracture toughness of the base alloys from 6.2 MN m^−3/2 to 9.8 MN m^−3/2.