Stainless steel binder for the development of novel TiC-reinforced steel cermets

Steel reinforced TiC composites are an attractive choice for wear resistance and corrosion resistance applications. TiC- reinforced 17-4PH maraging stainless matrix composites were processed by conventional powder metallurgy （P/M）. TiC-reinforced maraging stainless steel composites with 〉97% of theoretical density were fabricated. The microstructure, mechanical and wear properties of the composites were evaluated. The microstructure of these composites consisted of spherical and semi-spherical TiC particles. A few microcracks appeared in the composites, showing the presence of tensile stress in the composites produced during sintering. Typical properties, namely, hardness and bend strength were reported for the sintered composites. After heat treatment and aging, the increase of hardness was observed. The increase of hardness was attributed to the aging reaction in the 17-4PH stainless steel. The precipitates appeared in the microstructure and were responsible for the increase in hardness. The specific wear behavior of the composites was strongly dependent on the content of TiC particles, the interparticle spacing, and the presence of hard precipitates in the binder phase.     

Microstruetures and Mechanical Properties of TiC Particle Reinforced TiAl Composites by Spark Plasma Sintering

Using spark plasma sintering（SPS） technique, TiC particle reinforced γ-TiAl composites were prepared with varying weight fraction of TiC powders. The effects of the TiC fractions and distributions on the properties of the composites were investigated. The composite containing 7wt% TiC had the optimum three-point bending strength of 842 MPa,which was 200 MPa greater than that of the unreinforced γ-TiAl intermetallic. The degradation of the bending strength occurred in the composites containing more than 7wt% TiC and this was believed to be attributed to agglomerated particles of TiC, which acted as crack initiation and propagation sites. The increase of strength in TiC reinforced IMCs came from the grain refinement and the interaction of dislocations with the reinforcing particles. The bending strength of the IMC containing 7wt% TiC was theoretically estimated to increase by 85 MPa and 200 MPa, respectively, by the grain refinement and dislocation strengthening, the total of which was ahnost in accordance with the improvement in that of the unreinforced γ-TiAl intermetallic when considering normal estimation errors.     

Influence of Adding Ti Powder in Preform on Microstructure and Mechanical Properties of Al_2O_3p/Steel Composites by Squeeze Casting

To improve the mechanical properties of alumina particulates reinforced steel matrix composite, Ti powder was added into the alumina preform, a 5140 steel matrix composite was fabricated by squeeze casting, and the influences of Ti powder on the microstructure, hardness and bending strength of the composite were investigated, compared with the composite without adding Ti powder. Applied Ti powder and alumina particulates were 10-25 μm and 100-180 μm in size, respectively. Both composites were successfully fabricated, however Ti powder addition increased the infiltration thickness of the composite. In the Ti contained composite, a TiC film in micron scale is formed on the surface of alumina particles, many TiC aggregates are dispersed in the steel matrix without obvious remaining Ti powder. The hardness and the three-point bending strength of the composite reach 49.5 HRC and 1 018 MPa, respectively, which are 17.9% and 52.4% higher than those of the composite in the absence of Ti addition. Fracture morphology shows that the debonding of alumina particulates is eliminated for the composite in the presence of Ti addition. Sessile drop test shows the average wetting angle between 5140 steel and that of Ti coated Al_2O_3 is about 82.15°, much lower than the wetting angle 150° between steel and pure Al_2O_3. Therefore, the increase in the mechanical properties of the composite is attributed to the improvement of Al_2O_3 p/steel interface wetting and bonding by adding Ti powder in the preform.     

Processing and characterization of Cf/SiC composites

Carbon fiber-reinforced SiC composites were prepared by precursor pyrolysis-hot pressing （PP-HP） and precursor impregnation-pyrolysis （PIP）, respectively. The effect of fabrication methods on the microstructure and mechanical properties of the composites was investigated. It was found that the composite prepared by PP-HP exhibits a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface and the degradation of the fibers caused by a higher processing temperature. On the contrary, the composite prepared by PIP shows a tough fracture behavior, which could be rationalized on the basis of a weakly bonded fiber/matrix interface as well as a higher strength retention of the fibers. As a result, in comparison with the composite prepared by PP-HP, the composite prepared by PIP achieves better mechanical properties with a flexural strength of 573.4 MPa and a fracture toughness of 17.2 MPa.m^1/2.     

Improvement of Toughness of UHMWPE/PP Blends

Ultra-high molecular weight polyethylene (UHMWPE) was blended with polypropylene (PP) in order to ensure good processing. Inorganic rigid particles were also used to toughen UHMWPE/PP blends. CaCO₃ and a compound additive containing heat mixed polyethylene glycol 2000 and white diatomite were added to the blends. The crystalline, surface morphology and mechanical properties of the blends were investigated comprehensively. The toughness of the material is effectively improved. By contrast, the compound additive had a better result. When the content of additive was 15%, the elongation at the break increased by 279.2% and the fracture energy increased by 343.8% compared to the original samples.     

Enhanced Interfacial Adhesion in HDPE/HA Composites by Surface Modification of HA Particles via in situ Polymerization and Copolymerization

Hydroxyapatite （ HA ）- reinforced high density polyethylene （HDPE） was developed as a bone replacement material,In order to enhaace the interfacial bonding between HA and polyethylene and improve the mechanical properties of HDPE/ HA composites, the surface of the micron-sized HA particles was modified by in situ polymerization of butyl acrylate （ BA ） and in situ copolymerization of vinyl triethoxyl silane （ VTES ） and BA , then the modifwd HA particles were compounded with HDPE. The effects of the surface modification of HA on morphology and mechanical properties of HDPE/ HA composites were investigated. The experimental results show that the presence of HA particles does tuft inhibit the polymerization of BA . The poly（ butyl acrylate） （ PBA ） segments on the HA surface enhance the compatibility between HA and HDPE, improve the dispersion of HA particles in HDPE matrix, and enhance the interfacial adhesion between HA and matrix. Surface modifieations , especially by in situ copolymerization of VTES and BA, significantly increase notch impact strengths and marginal stiffness and tensile strengths of HDPE/HA composites. And it is found that there is a critical thickness of PBA coating on HA panicles for optimum mechanical properties of HDPE / HA composites.     

Mechanical Properties and Erosive Wear Resistance of Zirconia Toughened Al2O3-TiC Ceramics

The effect of ZrO2, content on the fracture toughness, flexural strength and Vickers hardness as well as the erosive wear resistan properties of zirconia toughened Al2O3-TiC ceramic composites has been investigated. The results showed that the improvement in fracture toughness and flexure strength of composites with the content of zirconia less than 50% and 10% in mass fraction respectively,is primarily attributed to stress-induced transformation toughening by the analyse of X-ray diffraction. The dependance of erosion wear resistance on the attak angle and the content of ZrO2, panicles of the composites was also revealed. It is found that the erosion rate of the composites has a sharp rise at a attack angle over 65°. This phenomenon is due to a brittle response to the erosion test by microsmictural observation on eroded surface.     

Sintering behavior, microstructure and properties of TiC-FeCr hard alloy

TiC based cermets were produced with FeCr, as a binder, by conventional P/M （powder metallurgy） to near 〉97% of the theoretical density. Sintering temperature significantly affects the mechanical properties of the composite. The sintering temperature of 〉1360℃ caused severe chemical reaction between TiC particles and the binder phase. In the TiC-FeCr cermets, the mechanical properties did not vary linearly with the carbide content. Optimum mechanical properties were found in the composite containing 57wt% TiC reinforcement, when sintered at 1360℃ for 1 h. Use of carbon as an additive enhanced the mechanical properties of the composites. Cermets containing carbon as an additive with 49wt% TiC exhibited attractive mechanical properties. The microstructure of the developed composite contained less or no debonding, representing good wettabifity of the binder with TiC particles. Homogeneous distribution of the TiC particles ensured the presence of isotropic mechanical properties and homogeneous distribution of stresses in the composite. Preliminary experiments for evaluation of the oxidation resistance of FeCr bonded TiC cermets indicate that they are more resistant than WC-Co hardmetals.     

Microstructures and Mechanical Properties of TiC Particle Reinforced TiAl Composites by Spark Plasma Sintering

Using spark plasma sintering(SPS)technique,TiC particle reinforcedγ-TiAl composites were prepared with varying weight fraction of TiC powders.The effects of the TiC fractions and distributions on the properties of the composites were investigated.The composite containing 7wt%TiC had the optimum three-point bending strength of 842 MPa,which was 200 MPa greater than that of the unreinforcedγ-TiAl intermetallic.The degradation of the bending strength occurred in the composites containing more than 7wt% TiC and this was believed to be attributed to agglomerated particles of TiC,which acted as crack initiation and propagation sites.The increase of strength in TiC reinforced IMCs came from the grain refinement and the interaction of dislocations with the reinforcing particles.The bending strength of the IMC containing 7wt% TiC was theoretically estimated to increase by 85 MPa and 200 MPa,respectively,by the grain refinement and dislocation strengthening,the total of which was almost in accordance with the improvement in that of the unreinforcedγ-TiAl intermetallic when considering normal estimation errors.     

Dynamic mechanical and thermal properties of cross-linked polystyrene/glass fiber composites

Cross-linked polystyrene/glass fiber composites were fabricated using cross-linked polystyrene (CLPS) as matrix and E-glass fiber as the reinforcement. Surfaces of E-glass fibers were modified by vinyl triethoxysilane (VTES), vinyl trimethoxysilane (VTMS) and γ-methacryloylpropyl trimethoxysilane (MPS). The treated glass fibers were analyzed by fourier transform infrared spectroscopy (FTIR). Dynamic mechanical thermal analysis (DMTA) and thermo-gravimetric analysis (TGA) were employed to investigate the effect of glass fibers surface modification on viscoelastic behavior and thermal properties. The morphology of fracture surfaces of various composites was observed by scanning electron microscopy (SEM). The results revealed that these coupling agents were connected to the surfaces of the fibers by chemical bonding. Dynamic mechanical properties as well as thermal stability of the composites were improved considerablely, but to varying degrees depending on the fiber modification. The diversities of improvement of properties were attributed to the different interfacial adhesion between CLPS matrix and the glass fibers.     

Fabrication and mechanical properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl composites

Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO₂ and Nb₂O₅, and the microstructure and mechanical properties were investigated. The results indicate the fine Al₂O₃ particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb₂O₅ content. The bending strength and fracture toughness reach to a maximum when Nb₂O₅ content is 6 wt%, under 642 MPa and 6.69 MPa·m^1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al₂O₃ particles.     

烧结温度和成分对Al_2O_3-TiC复合材料力学性能影响

以α-Al2O3粉、TiC粉为原料,采用热压烧结工艺制备了Al2O3-TiC复合材料,系统研究了烧结温度以及成分对Al2O3-TiC复合材料的组织结构和力学性能的影响规律.结果表明:α-Al2O3与TiC间没有发生化学反应,两相间具有很好的化学相容性.TiC的引入有利于提高Al2O3-TiC复合材料的力学性能.1 600℃热压烧结的Al2O3-20%TiC复合材料具有最佳的力学性能,其抗弯强度和断裂韧性分别达到509.45 MPa和5.27 MPa·m1/2,复合材料的断裂方式主要是沿晶断裂,同时伴有穿晶断裂.     

ZrO2含量对WC基复合材料的力学性能和微观结构的影响

摘要：以提高WC基复合陶瓷的断裂韧性和硬度为目标,利用ZrO2作为材料粘结剂和增强相,同时引入Al2O3添加相,采用热压烧结工艺成功制备了WC-ZrO2-Al2O3(WZA)复合刀具材料.在此基础上,添加一定量的VC作为晶粒生长抑制剂和助烧剂,以实现材料最大程度的致密化.并对热压后复合材料的硬度、抗弯强度和断裂韧性进行了测试和分析.探讨了ZrO2含量对材料微观结构和力学性能的影响,研究了复合材料断面断裂方式和材料相的组成.     

纳米TiC对Si3N4基复合陶瓷材料性能和微观结构的影响

用热压法制备了纳米TiC增韧补强的Si₃N₄基复合陶瓷材料,研究了不同TiC含量对复合陶瓷材料力学性能与微观结构的影响.结果表明：纳米TiC颗粒的添加对复合材料的力学性能的提高是有利的,当纳米TiC的质量分数为15%时,复合材料具备较优的力学性能,其抗弯强度、断裂韧性、HV硬度分别达到895MPa,8.03MPa.m1/2,15.06GPa;不同尺寸的Si₃N₄晶粒形成双峰结构,有利于复合材料性能的提高;其断裂机制为沿晶断裂和穿晶断裂的混合类型.     

Al_2O_3-TiC复合材料放电等离子烧结(SPS)致密化研究

用燃烧合成及放电等离子烧结法制备出致密Al_2O_3-TiC复合材料;分析了烧结温度与材料致密度、显微结构及力学性能的关系;真空气氛、1650℃、保温5min烧结试样的相对密度达99.8％,断裂韧性为4.61 MPa·m~(1/2);更高温度下烧结,气相反应加剧,不利于致密度进一步提高,力学性能也有所下降。沿晶断裂是其主要断裂方式。     

不同C加入量对原位合成TiC颗粒增强钢基表面复合材料组织和性能的影响

为解决金属材料耐磨性与韧性之间的矛盾,以ZG35CrMo为基体,以自蔓延高温合成TiC颗粒为增强体,采用真空消失模铸造工艺制备出表面质量优良的TiC颗粒增强表面耐磨钢基复合材料,对不同C加入量的颗粒增强复合材料的组织和性能进行分析研究.结果表明,制备的表面复合材料分为基体与合金层.当碳粉的加入量为化学计量比4∶1时,复合材料的组织和力学性能较好,加入量过量3∶1时会造成合金层及结合面性能的下降.     

掺杂对Al_2O_3/TiAl复合材料性能的影响

本研究采用Ti-Al-TiO2-La2O3体系,通过热压烧结工艺原位合成了Al2O3/TiAl复合材料.借助X射线衍射(XRD)、扫描电镜(SEM)等分析研究了材料的物相组成和微观组织结构,同时分别将掺杂La2O3和掺杂Fe2O3对合成Al2O3/TiAl复合材料微观结构和力学性能的影响进行了对比.结果表明:掺杂La2O3合成的Al2O3/TiAl复合材料基体尺寸相对掺杂Fe2O3合成产物较小,分散更加均匀,致密度更高.当La2O3掺杂量为3.93wt%时,Al2O3/TiAl复合材料的抗弯强度和断裂韧性达到最大值,分别为701.95MPa和7.79MPa·m1/2.由于稀土氧化物具有对基体和增强颗粒的净化,细化晶粒等作用,因此提高了TiAl基体与Al2O3增强颗粒结合强度,所以掺杂La2O3合成材料的力学性能相比掺杂Fe2O3合成的产物较高.     

合金元素对钢基复合材料组织和性能的影响

研究了Si,Mn合金元素加入量对自生TiC颗粒增强的钢基复合材料的组织和性能的影响．结果表明,在自生TiC颗粒增强钢基复合材料中,随着Si,Mn合金化元素的升高,复合材料基体组织将经历从单相珠光体到珠光体马氏体,再到单相马氏体的变化过程．相应地,复合材料铸态硬度从单相珠光体的HRC43．1变化到单相马氏体的HRC55．Si,Mn合金化元素的含量对热处理态复合材料的硬度也有明显影响,但对冲击韧性影响不大。