Microstructure and mechanical properties of SiC-particle-strengthening tri-metal Al/Cu/Ni composite produced by accumulative roll bonding process

In this study, a multilayer Al/Ni/Cu composite reinforced with Si C particles was produced using an accumulative roll bonding(ARB) process with different cycles. The microstructure and mechanical properties of this composite were investigated using optical and scanning microscopy and hardness and tensile testing. The results show that by increasing the applied strain, the Al/Ni/Cu multilayer composite converted from layer features to near a particle-strengthening characteristic. After the fifth ARB cycle, a composite with a uniform distribution of reinforcements(Cu, Ni, and SiC) was fabricated. The tensile strength of the composite increased from the initial sandwich structure to the first ARB cycle and then decreased from the first to the third ARB cycle. Upon reaching five ARB cycles, the tensile strength of the composite increased again. The variation in the elongation of the composite exhibited a tendency similar to that of its tensile strength. It is observed that with increasing strain, the microhardness values of the Al, Cu, and Ni layers increased, and that the dominant fracture mechanisms of Al and Cu were dimple formation and ductile fracture. In contrast, brittle fracture in specific plains was the main characteristic of Ni fractures.

Structures and Properties of Iron Matrix Composites with Tungsten Carbide Particle by EPC-V Process

In this paper the Expendable Pattern Casting with dry sand Vacuum(EPC-V) process is used to manufacture iron matrix composites with tungsten carbide particle.Microstructures of the composites layers were analyzed.The abrasive wear resistance of the composites layers were tested and compared with that of high chromium cast iron.The results show that the iron matrix composites with tungsten carbide particle have high hardness.The abrasive wear resistance of composites with tungsten carbide particle is higher than that of high chromium cast iron.The properties of the matrix materials have been improved remarkably.

Effect of TiC particle size on microstructure and mechanical properties of 1%TiC_p/W composites

The nano-TiCp/W and micro-TiCp/W composites containing 1% TiC(mass fraction) particles with average particle sizes of 50 nm and 1.5 μm were fabricated respectively by high energy ball milling and vacuum hot pressing(VHP) at 2 373 K,30 MPa,in a vacuum of 1×10-3 Pa. Microstructure and mechanical properties of the composites were examined at room temperature. The results show that both n-TiC and μ-TiC particles are homogeneously distributed in the as-sintered composites. The size of n-TiC particle is about 100 nm,and that of μ-TiC particle is about 1 μm. The additions of n-TiC and μ-TiC particles both result in higher mechanical properties compared with monolithic W. The improved mechanical properties may be mainly attributed to the grain size strengthening,dispersion strengthening and grain boundaries strengthening. The addition of n-TiC particles to tungsten is found to have beneficial effects on the mechanical properties than that of μ-TiC due to its small size.

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite （MMC） coating of approximately 350-400μm thickness was fabricated on a gray cast iron （GCI） substrate by plasma transferred arc （PTA） surface alloying of Ti-Fe alloy powder. Microhard- ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy （SEM） and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual anstenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures （473 K and 623 K）, and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam- ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc- ture and to the presence of TiC particles.

超音速火焰喷涂微纳WC-Cr_(3)C_(2)-CoNi涂层的结构与性能

为了研究双相碳化物金属陶瓷沉积行为对涂层结构性能的影响,分析了原始粉末、低碳钢基体上扁平粒子的表面形貌与截面结构,研究了超音速火焰喷涂微纳WC-Cr_(3)C_(2)-CoNi粒子的沉积涂层的组织结构、相结构和力学性能。研究结果表明:基体上沉积粒子呈现表面光滑浮凸的饼状,且粒子周边出现了径向溅射条纹,扁平粒子厚度远小于其径向尺寸。涂层截面显微组织结构呈现一定的层状特征,硬质相与粘结相、扁平粒子与扁平粒子、扁平粒子与基体及不同硬质相之间的界面结合良好。涂层相结构主要为WC、少量脱碳相、非晶相。Cr_(2)O_(5)涂层的显微硬度、弹性模量、断裂韧性、结合强度和磨损失重量分别为(13.19±0.52)GPa,(145.17±3.89)GPa,(2.59±0.64)MPa・m^(1/2),(38.41±0.51)MPa和(6.08±0.68)mg。相比WC-Co12涂层,超音速火焰喷涂WC-Cr_(3)C_(2)-CoNi涂层WC分解及其失碳相显著降低,力学性能明显提高。

Effects of sintering temperature on the microstructural evolution and wear behavior of WCp reinforced Ni-based coatings

This article focuses on the microstructural evolution and wear behavior of 50wt%WC reinforced Ni-based composites prepared onto 304 stainless steel substrates by vacuum sintering at different sintering temperatures. The microstructure and chemical composition of the coatings were investigated by X-ray diffraction （XRD）, differential thermal analysis （DTA）, scanning and transmission electron microscopy （SEM and TEM） equipped with energy-dispersive X-ray spectroscopy （EDS）. The wear resistance of the coatings was tested by thrust washer testing. The mechanisms of the decomposition, dissolution, and precipitation of primary carbides, and their influences on the wear resistance have been discussed. The results indicate that the coating sintered at 1175℃ is composed of fine WC particles, coarse M6C （M=Ni, Fe, Co, etc.） carbides, and discrete borides dispersed in solid solution. Upon increasing the sintering temperature to 1225℃, the microstructure reveals few incompletely dissolved WC particles trapped in larger M6C, Cr-rich lamellar M23C6, and M3C2 in the austenite matrix. M23C6 and M3C2 precipitates are formed in both the γ/M6C grain boundary and the matrix. These large-sized and lamellar brittle phases tend to weaken the wear resistance of the composite coatings. The wear behavior is controlled simultaneously by both abrasive wear and adhesive wear. Among them, abrasive wear plays a major role in the wear process of the coating sintered at 1175℃, while the effect of adhesive wear is predominant in the coating sintered at 1225℃.

添加粗晶WC对WC-Co硬质合金组织与力学性能的影响

以不同粒径WC粉、超细Co粉作为原料,通过低压烧结,制备添加粗晶WC的WC-Co硬质合金。采用XRD,SEM研究WC-Co硬质合金的物相组成及微观形貌,利用维氏硬度仪测试,计算合金的维氏硬度及断裂韧性。结果表明,由于粗晶WC的添加,裂纹在扩展过程中出现了明显的偏转,且穿晶断裂现象明显增多,对裂纹的扩展产生一定的阻力,使硬质合金的韧性提高。当添加的粗晶WC粒径为1μm时,合金的硬度由未添加粗晶WC时的1 930 HV降低至1 800 HV,断裂韧性由12.85 MPa·m1/2提高至15.05 MPa·m1/2,综合力学性能达到最佳平衡。

激光熔覆原位合成TiC-TiB_2/Ni基金属陶瓷涂层的组织和摩擦磨损性能

采用激光熔覆技术,以NiCrBSiC预合金粉末为原料,在TC4合金表面制备出以原位合成的TiC和TiB2颗粒为增强相的Ni基金属陶瓷涂层。测试了涂层的显微硬度。利用销-盘式摩擦磨损试验机,以YG8B硬质合金为对磨偶件(盘),评价了涂层的干滑动摩擦磨损性能。结果表明:涂层的硬度Hv为900～1100,摩擦系数为0.2～0.3,质量磨损率比TC4合金降低约1个数量级。

Effect of Ostwald ripening of carbide particles on mechanical properties of SCM435 steel during subcritical annealing

The Ostwald ripening of carbide particles occurs during the process of subcritical annealing in SCM435 steel, and the degree of ripening influences the microstructure and mechanical properties of the steel. The effects of Ostwald ripening were studied by simulating different soaking time at 680 ~C using SCM435 steel. The spheroidized specimens were analysed by conducting microstructure and mechanical tests. After increasing the soaking time from 2 to 6 h at 680 ~C during subcritical annealing, the number of carbide particles and the spheroidization ratio increased gradually, and the formability was improved. When the soaking time ranged from 6 to 8 h, the spheroidization ratio was similar; however, the number of carbide particles decreased, and the formability gradually worsened. Therefore, by comprehensively comparing the microstructures and mechanical properties, the optimum soaking time was determined to be 6 h at 680 ~C during subcritical annealing to obtain preferable cold heading. In addition, the carbide particles gradually coarsened when the soaking time was extended from 2 to 8 h. A formula was presented to quantitatively characterize the progress of Ostwald ripening of the carbide particles during the subcritical annealing of SCM435 steel, and the relative error was less than 8.02%.

热处理对离心铸造的WC-钢复合材料LGJW20组织的影响

研究了热处理工艺对离心铸造的WC-钢复合材料组织和性能的影响。结果表明,淬火后WC-钢复合材料的组织为马氏体、残留奥氏体和不同形态的碳化物,碳化物在不同淬火温度下以不同方式溶解。该复合材料的硬度随淬火温度的升高先上升后降低。

不同再生原料添加比例对WC-10%Co硬质合金性能的影响

配制含有不同比例再生原料的WC-10%Co硬质合金,研究了再生原料对WC-10%Co硬质合金的显微组织及力学性能的影响。结果表明在一定的配料比例下,该种加入再生原料的WC-10%Co硬质合金可以具有良好的显微组织和优良的力学性能。

Impact of Bauxite on Performance and Structure of SiC-mullite Brick

SiC- mullite brick is widely used in the upper and lower transitional zones of cement rotary kilns, due to excellent thermal shock resistance, and abrasion resist- ance. The investigation of different bauxites was made on the performance and micro-structure of SiC - mullite brick, especially thermal shock resistance. In two batches of bricks （ G1 and G2 ） , and two grades of bauxites （ L1 and I_2 ）, samples＇ physical and chemical properties were tested, and microstructure and phase composition were studied by SEM and XRD. The results show that raw material I2, containing large numbers of micro- pores smaller than 4 μm, has well developed mullite phase. While using L2 as aggregates and flues, SiC- mullite brick G2 has excellent thermal shock resistance. Therefore, for manufacture of SiC - mullite brick, not only chemical composition, bulk density and open porosi- ty of bauxite are important, but also its microstructure has to be considered, such as phase composition, crystal size and pore size distribution.

初始WC粉末对超细硬质合金组织与性能的影响

采用3种粒度分布特征存在差异的同类型WC原料粉末,通过不同球磨时间、不同烧结温度制备了WC-4%Co-0.4%Cr_(3)C_(2)合金,研究了合金微观组织结构及性能的变化。研究结果表明,采用粒度集中的WC粉末原料更易于获得WC分布均匀、晶粒尺寸均匀的超细硬质合金;当WC原料粒度分布宽、含有较多粗大桥接颗粒时,经过50 h球磨烧结后,可获得微观组织均匀的合金;球磨时间相同时,3种不同初始WC制备的合金微观组织结构随着烧结温度的升高趋向于更加均匀,合金中的WC晶粒生长更加完整,Co相分布更加均匀。3种WC原料,尽管在粉末形貌、粒度分布等方面存在差异,在球磨50 h、相同温度烧结条件下获得的硬质合金微观组织与力学性能趋于一致,长时间球磨可以弱化初始WC团聚对后续合金结构与性能的影响。

SiC_P/Mg复合材料的界面结构

采用真空压力浸渍法制备了碳化硅颗粒增强铸造镁合金（ＺＭ５）复合材料，碳化硅颗粒的平均尺寸为４μｍ，体积分数为４５％。通过透射电镜（ＴＥＭ）、能量色散谱仪（ＥＤＳ）研究了这种复合材料的ＳｉＣＰ／Ｍｇ界面微结构。实验结果表明：碳化硅颗粒与镁基体的界面结合紧密，界面区域存在合金元素铝的偏聚，并形成块状和细针状γ（Ｍｇ１７Ａｌ１２）相，这种γ相提高了界面结合强度。在ＳｉＣＰ／Ｍｇ界面区域存在高密度的位错缠结，这将对复合材料整体强度的提高作出贡献。另外，在有些ＳｉＣＰ／Ｍｇ界面上观察到氧化镁微晶层以及较大的氧化镁颗粒。

SiC_p／Zn基复合材料的制备与显微组织的观察

为探讨颗粒增强低熔点金属基复合材料的制备工艺和性能，扩大锌合金的应用范围，本项工作采用旋涡搅拌法制备了ＳｉＣｐ／Ｚｎ基复合材料，并讨论了搅拌工艺参数、增强颗粒表面处理对复合效果的影响。显微组织观察表明：ＳｉＣｐ分布均匀程度取决于颗粒的表面处理以及复合工艺参数的控制。ＳｉＣｐ经高温焙烧后，其表面获得一层稳定的ＳｉＯ２，从而有利于改善ＳｉＣｐ与基体锌合金的浸润性能。在基体中加入Ｍｇ等金属粉末，对于ＳｉＣｐ与基体的复合效果以及它的分布状态都起着良好的作用。此外，ＳｉＣｐ的加入速度，ＳｉＣｐ的粒径对复合效果也有较大影响。

多孔SiC陶瓷的两种制备方法

采用两种不同的方法制备多孔SiC陶瓷 ,讨论了其显微组织对性能的影响 ,探索了由天然木材经炭化、渗硅处理制造多孔SiC陶瓷的新方法 .研究结果表明 ,半干压法制得的SiC陶瓷的气孔率随SiC粒度的增大而降低 ,且强度升高 .由天然木材制得的多孔SiC陶瓷的气孔形状较规则 ,且分布均匀 ,其表观气孔率可达 4 0 %以上 ,是制备高气孔率SiC陶瓷的一种可行技术 .

等离子旋转电极雾化工艺制备FGH96合金粉末颗粒的组织

采用扫描电镜(SEM)、透射电镜(TEM)等多种手段对等离子旋转电极雾化工艺(PREP)制备的不同粒度FGH96合金粉末显微组织进行研究,结果表明:200～300μm的粉末颗粒凝固组织呈现典型的树枝晶特征,-50μm的粉末颗粒凝固组织呈现典型的胞状晶特征;粉末在快速凝固过程中会析出不同形貌的亚稳碳化物MC',不同形貌的MC'碳化物化学组成和点阵常数具有一定的差异。

新型碳化物颗粒增强铁基粉末冶金材料的组织与性能

制备了一种新型的碳化物颗粒增强铁基粉末冶金材料,采用光学显微镜、扫描电镜、能谱分析仪和力学性能试验机等研究了烧结温度和退火温度对其组织与性能的影响。结果表明:随着烧结温度升高,碳化物形貌从块状向针状转变;1 270℃烧结时的相对密度和硬度最高,1 240℃烧结时的抗弯强度和冲击韧度最高;脆性针状碳化物在晶界上以半连续网状析出,降低了材料的性能;1 200℃退火后,晶界上的针状碳化物分解并球化,其相对密度、硬度、抗弯强度和冲击韧度分别达到96.2%,44.5HRC,628MPa,3.8J.cm-2。

提高钻采工具用硬质合金性能的新技术

评述了近20年来,改善钻采工具用WC-Co硬质合金性能的主要技术方法。这些方法基本是围绕着同时提高合金的耐磨性和韧性、或者提高其中之一而不严重损害另一指标来进行的。其中,梯度硬质合金的方法能在一定程度上解决硬度与韧性的基本矛盾,效果较明显,但要求严格控制工艺参数。通过显微组织功能化设计得到的非均匀结构合金(DC合金),在改善断裂韧度、而不严重损害耐磨性方面具有最好的效果。粗晶低Co合金,由于采用高温碳化的粗颗粒WC,并且适当降低Co含量、以及严格控制杂质含量,提高了合金的导热性和韧性、减小了合金的热膨胀系数,因而改善了合金抗热疲劳能力和抗冲击能力,并且,对耐磨性无明显损害。添加金刚石颗粒则能显著提高合金的耐磨性,在添加量不大时,对合金的韧性无显著损害。通过在粘结相中添加合金元素,或控制成分和工艺使粘结相中析出弥散第二相,则能使合金强韧性和耐磨性得到显著提高。这些技术方法由于改善效果和成本的差异,适用于不同的应用场合。

TiC颗粒对半固态铝合金晶粒长大行为的影响

采用原位反应液相线铸造方法制备含有2.5%(体积分数)原位TiC颗粒的7075铝合金,在其固液两相区进行二次加热保温实验,淬火固定其半固态组织后,通过扫描电镜观察合金的晶粒长大规律,研究原位颗粒对晶粒长大行为的影响。结果表明,原位TiC颗粒不仅使合金铸态组织直接变为等轴晶组织,而且在合金的二次加热过程中对晶粒长大行为具有抑制作用,在600℃保温5、10和30min的相同条件下,TiCp/7075铝基复合材料晶粒尺寸比7075基体铝合金的减小30-40μm。