WC含量对Ni3Al-WC复合材料组织的影响

以WC，NiAl,NiB和Ni粉等球磨混合粉末烧结制备Ni3Al-WC复合材料焊条，用氩弧焊堆焊在1Cr25Ni20Si2耐热钢的表面形成Ni3Al-WC复合材料。当WC的含量从5%提高到30%时，在焊接过程中，由于熔池中溶解碳含量的增加，保护能力不断增强，溶池中的Al由部分氧化至完全不氧化，冷却后复合材料的组织也从碳化物包裹的氧化物/金属间化合物转变成碳化物/金属间化合物，获得无裂纹的焊接表面。     

碳化物特性对Ni3Al基表面强化复合材料组织与性能的影响

将真空常压烧结的方法制得的Cr3C2-Ni-Al和WC-Ni-Al复合焊丝氩弧堆焊于碳钢表面时,利用氩弧物理热和Ni-Al反应热,促使碳化物硬质颗粒与自生成的Ni3Al金属间化合物基体复合.XRD分析表明,在堆焊过程中两种焊丝中的Ni,Al均化合反应生成Ni3Al金属间化合物.微观组织与硬度试验表明,受各自物理特性(密度、熔点)的影响,两种碳化物硬质相在Ni3Al基体中分布均匀程度不同,其强化效果也迥异:WC仍以原始的大颗粒形态偏聚于焊层层间界面处,而起不到弥散强化作用;Cr3C2则发生分解,并反应析出条块状的Cr7C3相,均匀分布于Ni3Al基体中,很好地强化了基体材料.Cr7C3/Ni3Al复合材料的室、高温硬度远高于传统高温耐磨材料stellite合金.该合金有望成为一种新型的高温耐磨表面强化材料.     

真空熔覆WC颗粒增强复合涂层中WC溶解行为的研究

研究了真空熔覆条件下三种不同成分镍基WC复合涂层中WC颗粒的溶解行为.结果表明:Ni60A-WC复合涂层中,WC的溶解从边缘发生,以复合碳化物Fe6W6C的析出为主;Ni25B-WC复合涂层中,WC溶解方式表现为整体的"疏松分离"、部分WC的桥接及团聚;Ni22AA-WC复合涂层中,WC仅发生局部的疏松溶解.WC中W,C和基体中w,C含量的浓度差大,基体中Cr,Fe含量高,都会加速WC颗粒的溶解行为.     

激光熔覆(WC+W2C)p/Ni基合金复合涂层的微观结构特征

运用XRD、SEM及显微硬度试验等手段研究了激光熔覆Co包铸造（WC W2C）p增强Ni基合金复合涂层的微观组织特征，分析了Co包铸态（WC W2C）p 在激光熔覆过程中的冶金行为，研究结果表明：在激光熔覆过程中，（WC W2C)p的Co包覆层完全熔化，（WC W2C）p本身也发生部分熔解，其稳定性随W2C/WC比增大而降低；当熔池凝固时，（WC W2C）p在涂层中的分布主要受激光熔池中存在的强烈对流和颗粒/凝固前沿相互作用所控制；依赖于局部成分，涂层中形成变成分的η1-M6C（M=Co、W、Ni)型碳化物，优先分布（WC W2C）p表面；涂层基体的典型组织由分布在γ-Ni M23C6为主加硼化物Ni4B3、Ni3B和碳化物M7C3的伪多元共晶中的η1-W6C组成。     

高速电弧喷涂Fe-Al/WC复合涂层的高温摩擦磨损特性

采用滑动磨损试验方法研究在室温至650℃温度下高速电弧喷涂Fe—A1／WC金属间化合物复合涂层与Si3N4陶瓷球配副时的摩擦磨损特性，并探讨复合涂层的高温摩擦磨损机理。结果表明，随着试验温度的升高，Fe—Al／WC复合涂层的摩擦系数降低，而磨损率仍保持在较低的水平。高温下复合涂层滑动摩擦系数降低的主要原因是由于磨损面发生摩擦氧化反应而形成的起到固体润滑的作用氧化物保护层。剥层磨损是Fe—Al／WC复合涂层高温磨损的主要机理。涂层中Fe3Al和FeAl金属间化合物相较高的高温强度和硬度，能有效地阻碍裂纹的产生、扩展及扁平颗粒的断裂，从而使复合涂层表现出优异的高温耐磨性。650℃时Fe—Al／WC复合涂层的磨损率有所提高，这可能与高温下涂层表面WC颗粒的氧化和脱碳分解有关。     

添加Co对碳化钨颗粒增强表层复合材料性能的影响EI北大核心CSCD

制备WC-Co表层增强复合材料,观测复合层的显微组织和基体中的生成相,研究了添加Co对碳化钨颗粒增强表层复合材料性能的影响。结果表明:Co的加入使复合层中的基体组织中产生了细小粒状珠光体和屈氏体,降低了材料的脆性倾向,提高材料整体性能。金属液浸入预制层后,沿基材至复合层表面方向,金属液的温度递减,热扩散作用小,增加复合层内部基体成分不均匀性。当基体中的W、C原子浓度升高,基体中析出η型Co_3W_3C碳化物。在复合层冷却至1200℃之前,基体能够与碳化钨颗粒发生界面反应生成Co_3W_3C碳化物,提高基体的硬度,从而提高复合材料的耐磨性。     

Ni60A+WC增强梯度涂层中WC的溶解与碳化物的析出特征EI北大核心CSCD

采用等离子熔覆工艺制备了多层Ni60A+WC增强Fe基梯度涂层,增强相Ni60A+WC比例按10%(质量分数)逐层递增,研究了梯度涂层中WC颗粒的溶解及碳化物析出。结果表明:等离子熔覆加热阶段梯度涂层各层中WC颗粒均发生溶解,溶解的特征与WC大小及其内部缺陷有关,据此可将WC的溶解分为扩散式、芯部溶解式、溃散式、及扩散-芯部溶解复合式四种类型;在等离子熔覆凝固阶段,各层均析出富W型碳化物,析出位置及形貌与Ni60A+WC在每层的熔覆量有关,随着熔覆量的增加,富W型碳化物的析出特征依次为沿晶界呈网状→颗粒状→颗粒状+块状→小块状+簇团状→大块状+等轴状析出。析出的碳化物随着Ni60A+WC熔覆量的增加而增加且在各层中分布较均匀,测得梯度涂层的宏观硬度随着层数的增加呈线性递增分布。     

钎焊WC-Ni基复合涂层的耐腐蚀性能

钎焊法制备WC复合涂层可以克服热喷涂层的许多缺点,但目前对其在中性NaCl介质中的腐蚀行为研究不多。在碳钢表面真空钎焊制备了WC-Ni复合涂层,采用X射线衍射(XRD)分析了WC-Ni复合涂层表面的物相;通过动电位极化曲线考察了其在3%NaCl溶液中的腐蚀电化学行为;通过场发射扫描电镜(FEGSEM)结合EDX能谱仪观察了不同极化电位处理的涂层的表面形貌和化学组成;采用电感耦合等离子体发射光谱分析了不同极化电位下溶解的金属离子浓度。结果表明:钎焊WC-Ni复合涂层主要是由WC,Ni,NiW,Ni2W4C,Cr3NiB6等物相组成,没有W2C等脆性相;阳极极化曲线上出现2个电流密度平台,分别对应Ni,Cr的氧化物膜的形成和W氧化形成WO3膜层,低电位时主要存在Ni的活性溶解,高电位时同时存在Ni,Cr,W等元素的活性溶解;该涂层耐腐蚀性能较好,硬质相WC的脱落减少,耐磨性提高。     

热处理对Fe-Al/WC复合涂层的组织及磨损性能的影响

研究了300,450,550,650,800℃热处理对高速电弧喷涂Fe-Al/WC金属间化合物复合涂层的组织和滑动磨损性能的影响.结果表明,热处理后复合涂层中将析出Fe2W2C 和 Fe6W6C弥散相.450～650℃热处理后,部分Fe3Al转变成FeAl造成的点阵畸变以及Fe2W2C 和 Fe6W6C的弥散强化作用,使复合涂层的显微硬度明显提高.通过热处理提高Fe-Al/WC复合涂层的显微硬度,将提高复合涂层的耐磨性.     

WC在WC/灰铸铁复合材料基体中的溶解

为了对WC/Fe复合材料的界面设计和控制提供理论指导, 论文分析了WC在WC/灰铸铁复合材料基体中的溶解热力学, 通过差热分析、 光学显微镜、 扫描电镜和X衍射等测试方法研究了WC与灰铸铁基体之间的界面, 对WC颗粒在基体中的溶解过程进行了探讨。研究结果表明: WC颗粒与HT300基体润湿良好, 当系统最高温度为1450℃时, WC颗粒的表面有明显被溶解的痕迹, WC颗粒在HT300基体溶液中发生明显溶解的开始温度约为1281℃; 当系统温度升高到某一温度时, WC发生分解反应(2WCW₂C＋C), 元素扩散将促进WC颗粒的溶解。      

Cr7C3 / Ni3Al 复合材料制备过程中碳化铬的溶解再析出行为

将真空常压烧结方法制得的Cr₃C₂-Ni₂Al 复合焊丝堆焊于碳钢表面。分析表明, 在堆焊过程中, 利用氩弧物理热和Ni-Al 反应热, Ni 与Al 化合反应生成Ni₃Al 金属间化合物, Cr₃C₂ 则发生分解, 除少部分[ C]与[Cr ]固溶于Ni₃Al 基体中外, 大部分反应析出更稳定的Cr₇C₃ 相, 其尺寸取决于堆焊层中不同区域的冷却环境,较为均匀地分布于Ni₃Al 基体中。由于Cr 在Ni₃Al 中的固溶度远大于C , 加之Cr₃C₂ 转化为Cr₇C₃ 也造成部分富余的C , 结果造成在该Ni₃Al 表面强化材料焊层中形成石墨相, 其密度轻、熔点高, 主要偏聚于焊层表层。Cr₇C₃ / Ni₃Al 复合材料的室温、高温硬度远高于传统高温耐磨材料Stellite 合金, 该材料有望成为一种新型的高温耐磨表面强化材料。      

WCP/Fe-C 复合材料的界面反应和基体合金化研究

利用离心铸造成型碳化钨颗粒(WCP ) 增强Fe-C 基体合金的复合结构空心圆柱体, 采用宏观测量、X 射线衍射分析和扫描电镜(SEM ) 与能谱(EDS) 的微观分析, 对WCP/Fe-C 界面反应和基体合金化研究。结果表明, 在转速800～ 1200 r/m in离心铸造机上获得了外径167mm , 内径87mm , 高67mm 的空心圆柱体, 其表面层为16～ 20mm 大断面WCP/Fe-C 复合材料, 芯部为Fe-C 基体合金。铸造碳化钨颗粒(CTCP ) 的表面被高温Fe-C 基体合金熔融体部分溶解, 甚至解体; 原位( in2situ) 自生成细小短棒状WC 和W₂C 先共晶析出相; 远离CTCP , 分布游离的细小颗粒状和网状WC、W ₂C、Fe₃W ₃C₂Fe₄W ₂C、Cr₇C₃ 和Fe₃₂C 碳化物。由于CTC_P 部分溶解和扩散作用, 复合结构空心圆柱体的Fe-C合金基体被不同程度合金化。      

耐磨耐蚀Ni-Al金属间化合物基复合保护层的研制

用粉末冶金法制备WC／Ni3Al复合材料焊条，堆焊于1Cr25Ni20耐热钢的表面，获得的复合材料的耐磨粒磨损性能是45钢的3倍以上，耐硫化腐蚀性高于1Cr25Ni20耐热钢1倍，高于钴基合金Stellite6约50％，用其制作火电厂燃烧室的喷口钝体，使用寿命较原8Cr26Ni4Mn3大幅度提高，可达到8个月以上。     

Influence of Ni Interlayers on the Mechanical Properties of Ti6Al4V/(WC-Co) Friction Welds

Ni interlayers were introduced prior to dissimilar friction welding of Ti6Al4V base material to three cemented carbide substrates. The fracture strength of Ti6Al4V/(WC-6 wt% Co) welds were poor and were markedly improved when 20-µm thick Ni interlayers were introduced prior to dissimilar friction welding. These results were only produced when the (WC-6 wt% Co) cermet was electroplated prior to friction welding. When the Ti6Al4V alloy was electroplated prior to friction welding, fractured WC particles and cracking were observed in the (WC-Co) carbide substrate. The fracture strengths of Ti6Al4V/(WC-11 wt% Co) and Ti6Al4V/(WC-24 wt% Co) welds were not improved when 20-µm thick Ni interlayers were introduced prior to friction welding. During mechanical testing, the Ni layer retained at the dissimilar joint interface created a region of weakness.     

The microstructure and its properties of Ni3Al based composite

 Composites of B-doped ductile Ni₃Al alloy matrix with no-oxide WC ceramic powders were produced by mechanical alloying, half-sintering and build-up welding. WC powders form non-continuous hardening phases, which are distributed in Ni₃Al matrix, wetting well with the matrix. The hardness and the structure stability are retained to temperatures of at least 850°C. After build-up welding, most of the NiAl phase left after sintering was changed into other phases and some graphite was precipitated in the matrix. The sand-laden water wear test showed expected results. Received: 12 October 1998/Accepted: 2 November 1998     

Microstructure Formation of HVOF Sprayed WC-Ni Coatings Deposited on Low Alloy Steel

A low alloy steel was coated with WC-Ni by the High Velocity Oxy-Fuel process, in order to increase the wear resistance and corrosion resistance of the material. The microstructure of the coating was determined using various techniques, such as SEM, TEM, EDAX, EPMA and X-ray diffraction methods

During spraying, the WC-Ni powder granules were heated to above the melting point of Ni, before arriving at the substrate surface. The molten Ni dissolves WC rapidly, forming Ni-W-C liquid alloys. Some C and some W are removed from the WC particles by oxidation. When each droplet strikes the steel substrate, a pancake-shaped splat forms, and solidifies with a rapid cooling rate. The structure is built up by the progressive deposition of the splats to produce a continuous coating. The Ni-W-C metallic matrix of the coatings consists of two basic structural types, Ni-rich material with a grain size of 10 - 100 nm, and a FCC crystal structure with a lattice parameter larger than that of Ni indicating the presence of dissolved W and C. The other metallic phase is W-rich, with a grain size less than 10 nm, and in some regions it appears to be amorphous. Dispersed within this material there were sometimes small crystals of W and W₂C. In the initial powder the volume fraction of WC was about 75%, but in the sprayed coating the volume fraction of the WC was reduced to about 20%. This is partly due to loss of W by oxidation, but chiefly due to dissolution of W into the metallic phase.     

Toughening effects of WC/Co particles and compressive surface stress on (Al2O3–WC/Co)/TiC/Ni graded materials

A graded material of the (Al2O3–WC/Co)/TiC/Ni was prepared by using the self-propagating high-temperature synthesis-aided hot isostatic pressing process. The WC/Co particles were added to the outer Al2O3 layer in order to activate the heterophase toughening effects and control the thermal expansion mismatch between the outer and inner layers. SEM and TEM observations show a clustering structure of the WC/Co cermet in the Al2O3 matrix. The residual stress introduced by the compositionally graded structures was analysed using FEM calculation and X-ray diffraction. Measurements of the indentation toughness and R-curve behaviour indicated that the compressive surface stresses and WC/Co particles can significantly strengthen and toughen the Al2O3 ceramics. The indentation toughness of the (Al2O3–WC/Co)/TiC/Ni at the surface was 13.1 MPa m1/2, while those of the (Al2O3–WC/Co) uniform composite and the monolithic Al2O3 were 7.3 and 4.0 MPa m1/2, respectively. It was found by SEM observation of the crack propagation induced by indentation, thatthe crack deflection, bridging, blunting and arresting occurred at the WC/Co clusters. © 1998 Chapman & Hall