激光熔覆WC/316L复合涂层结构及磨损性能

为改善激光熔覆过程中WC增强金属基复合涂层分解与分布不均匀的问题,采用激光熔覆技术制备了50%WC含量的WC/316L复合涂层,分别采用扫描电子显微镜(SEM)、显微维氏硬度计、摩擦磨损试验机表征了熔敷层的组织形貌、硬度与摩擦磨损性能。结果显示,低热输入量可以防止WC颗粒下沉,提升熔覆层厚度方向上的WC颗粒分布均匀性;但WC的平面分布均匀性较差,同时低热输入导致WC颗粒结合较弱,易发生脱落;熔覆过程中,粉末中15%的WC发生分解。研究表明,通过降低激光热输入量,可以制备WC厚度方向较为均匀的复合涂层,提升熔覆层耐磨性,但是需要优化WC平面分布均匀性与WC颗粒结合性能。

Statistical Analyses of the Strengths of Particulate Reinforced Metal Matrix Composites(PRMMCs)Subjected to Multiple Tensile and Shear Stresses

For design and application of particulate reinforced metal matrix composites(PRMMCs),it is essential to predict the material strengths and understand how do they relate to constituents and microstructural features.To this end,a computational approach consists of the direct methods,homogenization,and statistical analyses is introduced in our previous studies.Since failure of PRMMC materials are often caused by time-varied combinations of tensile and shear stresses,the established approach is extended in the present work to take into account of these situations.In this paper,ultimate strengths and endurance limits of an exemplary PRMMC material,WC-Co,are predicted under three independently varied tensile and shear stresses.In order to cover the entire load space with least amount of weight factors,a new method for generating optimally distributed weight factors in an n dimensional space is formulated.Employing weight factors determined by this algorithm,direct method calculations were performed on many statistically equivalent representative volume elements(SERVE)samples.Through analyzing statistical characteristics associated with results the study suggests a simplified approach to estimate the material strength under superposed stresses without solving the difficult high dimensional shakedown problem.

Simplified prediction model for elastic modulus of particulate reinforced metal matrix composites

Some structural parameters of the metal matrix composite, including particulate shape and distribution do not influence the elastic modulus. A prediction model for the elastic modulus of particulate reinforced metal matrix Al composite was developed and improved. Expressions of rigidity and flexibility of the rule of mixing were proposed. A five-zone model for elasticity performance calculation of the composite was proposed. The five-zone model is thought to be able to reflect the effects of the MMC interface on elastic modulus of the composite. The model overcomes limitations of the currently-understood rigidity and flexibility of the rule of mixing. The original idea of a five-zone model is to propose particulate/interface interactive zone and matrix/interface interactive zone. By integrating organically with the law of mixing, the new model is found to be capable of predicting the engineering elastic constants of the MMC composite.

Preparation and Mechanical Properties of-SiC Nanoparticle Reinforced Aluminum Matrix Composite by a Multi-step Powder Metallurgy Process

β-SiC nanoparticle reinforced A1 matrix （nano-SiCp/A1） composite was prepared by a multi- step powder metallurgy strategy including presureless sintering, hot compacting process and hot extrusion. The microstructures of the as-prepared composites were observed by scanning electronic microscopy （SEM）, and the mechanical properties were characterized by tensile strength measurement and Brinell hardness test. The experimental results revealed that the tensile strength of the composite with the addition of 5wt%/3-SIC nanoprtieles could be increased to 215 MPa, increasing by 110% compared with pure A1 matrix. Comparative experiments reflected that theβ-SIC nanoprticles showed significant reinforcement effect than traditional a-SiC micro-sized particles. The preparation process and sintering procedure were investigated to develop a cost effective preparation strategy to fabricate nano-SiCp/A1 composite.

Microstructure and Strength of Laser Welds of Sub-micron Particulate-reinforced Aluminum Matrix Composite Al_2O_(3p)/6061Al

The microstructure of laser welds of sub-micron particulate-reinforced aluminum matrix composite Al_2O_(3p)/6061Al and the weldability of the material were studied. Experimental results indicated that because of the huge specific surface area of the reinforcement, the interfacial reaction between the matrix and the reinforcement was re- strained intenslvely at elevated temperature and pulsed laser beam. The main factor affecting the weldability of the com- posite was the reinforcement segregation in the weld resulting from the push of the liquid/solid interface during the soli- dification of the molten pool. The laser pulse frequency directly affected the reinforcement segregation and the reinfor- cement distribution in the weld, so that the weldability of the composite could be improved by increasing the laser pulse frequency. On the basis of this, a satisfactory welded joint of sub-micron paniculate-reinforced aluminum matrix com- posite Al_2O_(3p)/6061Al was obtained by using appopriate welding parameters.

Evaluation of Filler Distribution in Particulate Reinforced Composites

Aluminum matrix particulate reinforced composites are of significant interest to industry, but it’s difficult to provide stable properties for this group of material. The mechanical properties of metal matrix composites are deeply influenced by the distribution of reinforcement particulates in the matrix. In this paper uniformity of SiC particles distribution in Al-based composites produced by stir casting and powder metallurgy technique is assessed. Analysis is carried out by means of classical and computer quantification metallographic image analysis methods. In addition, we suggest setting hardness distribution in cross section of samples as an indicator of reinforcement distribution uniformity in the matrix.

Simplification and improvement of prediction model for elastic modulus of particulate reinforced metal matrix composite

In this paper, we proposed a five-zone model to predict the elastic modulus of particulate reinforced metal matrix composite. We simplified the calculation by ignoring structural parameters including particulate shape, arrangement pattern and dimensional variance mode which have no obvious influence on the elastic modulus of a composite, and improved the precision of the method by stressing the interaction of interfaces with pariculates and maxtrix of the composite. The five- zone model can reflect effects of interface modulus on elastic modulus of composite. It overcomes limitations of expressions of rigidity mixed law and flexibility mixed law. The original idea of five zone model is to put forward the particulate/interface interactive zone and matrix/interface interactive zone. By organically integrating the rigidity mixed law and flexibility mixed law, the model can predict the engineering elastic constant of a composite effectively.

电冶熔铸WC/钢复合材料中WC的溶解行为

用电冶熔铸工艺制备不同WC含量的WC/钢复合材料,研究了WC颗粒在复合材料钢基体中的溶解行为和影响因素。结果表明:随着WC含量的增加,碳化物从钢基体晶界处分布逐渐转向晶内分布;随着WC颗粒尺寸的增大,在WC颗粒与钢基体界面处形成一层反应物,它阻止了WC颗粒在钢基体中的进一步溶解,同时也提高了两相界面的结合强度。通过调整电冶熔铸工艺参数和WC颗粒的尺寸及含量,可以控制WC颗粒在复合材料中的溶解行为。

电冶熔铸WC/钢复合材料组织及碳化物演变的研究

采用电冶熔铸法制备了以GCr15轴承钢为基体,WC颗粒为硬质相的WC/钢基复合材料。借助金相分析、扫描电镜、X射线衍射、透射电镜及能谱分析等方法研究了该材料熔铸态显微组织结构及其演变过程。结果表明:随着加入WC含量和颗粒尺寸的不同,其凝固后组织结构不同。当加入10%WC时,WC颗粒大多溶解于钢液中,冷却后沿晶界析出断续网状复式碳化物,同时基体中析出细小的Cr7C3、β-WC1-x、Fe3W3C颗粒;当加入20%WC时,大颗粒WC外围部分溶解形成Fe3W3C反应层,钢基体中析出共晶碳化物;当加入35%WC时,显微组织主要是以γ-Fe+WC、γ-Fe+Fe3W3C共晶组织为主,多数呈树枝状和锚状,少数为不规则块状;当加入40%或50%WC时,WC颗粒基本保留原始形状且稳定不易溶解,多数呈三角状、矩形,均匀分布。

激光-TIG复合熔注制备WC_p/Al复合材料层的微观组织

采用激光-TIG复合熔注工艺，在铝合金表面制备WCp／Al表面复合材料层。通过优化激光功率、TIG电流、扫描速度和送粉率等工艺参数，可以获得0．5～4.3mm厚的表面复合材料层。采用XRD、SEM、EDS等手段对表面颗粒强化层的微观组织和成分进行研究。结果表明：熔注层基体的微观组织为过共晶组织；熔注层不同位置的过共晶相具有不同的形貌，熔池上部主要为含有十字花状、鱼骨状、蝶状先共晶相（W1-xAlx）Cy的过共晶组织，而底部的先共晶相呈现块状形态。

电冶熔铸WC-Co/钢复合材料组织和性能的研究

用回收的废WC Co硬质合金作原料,采用电冶熔铸法制备了新型的WC/钢基复合材料。借助金相分析、扫描电镜及X射线衍射等方法研究了该材料铸造原始态和退火态的微观组织结构,还测试了主要力学性能。材料中的硬质相和钢基体相的相互溶解,使两相实现了冶金结合,形成含W和Co的碳化物,但形态不佳。增加电磁搅拌可使枝晶"破碎";经退火处理和锻造可以改善材料中的不良组织,使硬质相碳化物粒子均匀地分布在钢基体中,冲击韧度也得到提高。

铸造WC/钢铁基复合材料研究进展

对国内外用铸造法制备的WC颗粒增强钢铁基复合材料研究进展进行了综述,包括了WC颗粒的选择,制备方法和工艺。重点分析了复合材料中增强相和基体相间的相互作用和界面问题,并讨论了优化制备工艺和提高材料性能的途径。文章指出,铸造WC钢铁基复合材料是一种具有广泛应用前景的新型复合材料,在工艺性和性价比上都有很大优势,值得进一步研究与开发。

离心铸造WC_p/钢基复合材料的组织及断口特征

研究了离心铸造工艺制备的WCp/钢基复合材料的显微组织及断口形貌。结果表明:离心铸造显著的细化了基体材料的组织结构,WC颗粒在复合材料中均匀分布,复合材料断口特征主要表现为脆性断裂,在断口上可以观察到WC颗粒开裂和界面脱粘现象。

WC/FY-1烧结锻造钢基复合材料性能

采用烧结锻造和合金化技术制备了WC/FY 1烧结锻造钢基复合材料,对材料的组织结构和性能进行了研究·结果表明,FY 1母合金的加入使FY 1烧结锻造钢的密度、强度、硬度及基体的耐磨性大幅度提高,冲击韧性下降·FY 1母合金在WC/FY 1钢的烧结过程中产生了部分液相,因而促进了致密化过程·WC的加入明显地提高了FY 1烧结锻造钢的耐磨性,其中15%WC/FY 1烧结锻造钢的磨损量仅为目前使用的导向辊材料W18Cr4V磨损量的1/5·所制备的WC/FY 1烧结锻造钢基复合材料达到高速线材轧机的导向辊用材的性能要求,因而有望在实际中获得应用·

WC_p增强钢基复合材料的三体磨损性能

在室温条件下,选用三体磨粒磨损试验机,石英砂磨料,研究增强相WC颗粒直径对WCp增强钢基表层复合材料磨损性能的影响,以20%Cr高铬铸铁作为标样,计算相对耐磨性值。结果表明,WCp增强钢基表层复合材料相对于20%Cr高铬铸铁的相对耐磨性,随其增强相WC颗粒直径的变小而降低,当增强相WC颗粒直径大于150μm时,相对耐磨性值达到5左右,而当增强相WC颗粒直径小于100μm时,相对耐磨性值降低到1左右,即与20%Cr高铬铸铁的抗磨粒磨损性能相接近。

离心铸造工艺制备WC颗粒增强钢基回转体零件研究

通过改进现有悬臂式离心铸造机,成功制备了外径200 mm、内径140 mm、长150 mm的碳化钨颗粒增强钢基回转体复合材料。分析了增强颗粒在离心铸造中的受力情况,推出液态金属中的颗粒在离心力场下的运动规律。采用光学显微镜、扫描电镜和X射线衍射,分析了复合层中碳化钨颗粒的分布规律,以及复合层的物相组成。结果表明,碳化钨颗粒体积分数在复合层中由内向外逐渐增加,其表层碳化钨颗粒复合层厚度约5 mm,颗粒与基材结合良好,没有夹杂、裂纹等缺陷;颗粒与颗粒之间无缠结团聚现象;颗粒周围部分溶解,复合层中存在Fe3W3C相,颗粒与基材间形成冶金结合。

复合电冶熔铸WC颗粒增强钢基复合材料的显微缺陷研究

采用复合电冶熔铸工艺制备了WC颗粒增强钢基复合材料,该工艺具有高能球磨混粉均匀、电渣重熔精炼净化、电磁搅拌颗粒分散、水冷结晶逐层快速凝固等特点,熔炼过程中有利于气体排出、夹杂物的去除、WC颗粒的分散等,较好地解决了颗粒团聚和聚集问题.得益于较快的冷却速度,WC颗粒被钢液吞没,尽可能地避免了枝晶偏析,使晶粒得到细化.所制备的复合材料孔隙少、致密高、无夹杂,WC颗粒分布均匀,缺陷很少.

电渣熔铸WC/Cr12Mo1V1钢基复合材料的摩擦磨损特性

采用电渣熔铸技术制备了WC/Cr12Mo1V1钢基复合材料,并对其显微结构、硬度和摩擦磨损特性进行了研究。结果表明,WC颗粒分布较为均匀,部分溶解于钢基体中。冷却后析出Fe3W3C复式碳化物,提高了相界面结合强度和材料的强韧性。而且轧辊外部的硬度和耐磨性均高于芯部,满足轧辊性能要求。

感应电渣熔铸WC颗粒增强钢基复合材料的力学性能研究

采用电渣熔铸技术,制备了以5Cr Ni Mo模具钢为基体,WC颗粒为硬质相的钢基复合材料。利用扫描电子显微镜、冲击试验机、摩擦磨损试验机等研究了复合材料的冲击韧度、断口形貌、摩擦系数、磨损量和磨损机制。结果表明,复合材料冲击韧度值较小,断裂方式均是脆性断裂。顶部和中部试样分布着沿晶或穿晶二次裂纹,为解理断裂。尾部试样部分区域具有一些韧性特征,断口为细韧窝和部分沿晶断口。热处理后试样的耐磨性得到很大提高,在干滑动磨损条件下,试样的磨损机制主要是粘着磨损引起的表面剥落及磨屑充当第三体引起的磨粒磨损。