Cr含量对Mo2FeB2基金属陶瓷组织和性能的影响

采用真空液相烧结法制备了Mo2FeB2基金属陶瓷,研究了Cr添加量(质量分数0～11％)对其组织和力学性能的影响.结果表明:Cr的添加使金属陶瓷出现Fe23B相,Cr完全固溶于Fe基粘结相中;随着Cr添加,硬质相晶粒逐渐由柱状晶向等轴晶转变;当Cr添加量为9％时,金属陶瓷的孔隙率最小,致密度最高,当Cr添加量大于9％时...     

WC含量对Ti(C,N)基金属陶瓷组织和性能的影响研究

用传统的粉末冶金方法制备了不同WC含量的超细Ti(C,N)基金属陶瓷试样,运用SEM,EDX等手段对材料的显微组织进行了表征分析,并用这些显微组织的特征和差异解释了材料宏观力学性能的特点.结果表明,金属陶瓷的组织为典型的两相结构特征,其中陶瓷相的芯、壳结构(core/timstructure)与溶解析出机制有关.少量WC的加入能提高材料的力学性能.断口SEM分析表明:断裂机理为典型的混合型断裂(穿晶断裂和沿晶断裂),金属相存在着明显撕裂的痕迹.     

Cr3C2和VC对Ti(C,N)基金属陶瓷中环形相的价电子结构和性能的影响

根据固体与分子经验电子理论，计算了Ti(C，N)基金属陶瓷中界面环形相的价电子结构，讨论了其价电子结构与塑性间的关系。当材料晶体结构相同时，Σna可用来比较其塑性的相对高低。Cr在环形相(Ti，Mo)(C，N)中的固溶，可使其塑性增强，V在环形相中的固溶将使其塑性变差。在计算的基础上进行实验，实验结果表明：Cr3C2的适量加入确实有利于提高金属陶瓷的强度，最终所制备出金属陶瓷的强度比典型成分体系材料的提高了1倍以上；尽管VC的加入能使材料的晶粒得到有效地细化，但它使环形相塑性降低，使金属陶瓷的抗弯强度略有增加。     

Mo对Ti(C,N)金属陶瓷组织结构和力学性能影响

以原始粉体作为原料,采用传统的粉末冶金方法制备Ti(C,N)基金属陶瓷,研究不同钼含量对Ti(C,N)金属陶瓷的显微组织结构和力学性能的影响。根据设计的成分配方,采用传统的粉末冶金方法按照优选的工艺来制备一系列的金属陶瓷试样,在不改变金属陶瓷硬度和抗热震能力的基础上,尽量提高其硬度和其他力学性能。对烧结试样的表面进行必要的处理,采用X射线衍射(XRD)、金相显微镜、维氏硬度仪等表征方法研究了Mo含量对Ti(C,N)基金属陶瓷组织结构和力学性能的影响。实验结果表明:Mo含量在(5wt%～10wt%)范围内,材料的相对密度随Mo含量的增加而提高,而Mo含量在(5wt%～10wt%)范围内,材料的相对密度随Mo含量的增加而降低,Mo含量为10wt%时,金属陶瓷的相对密度最高。在Mo含量一定的范围内(5wt%～15wt%),随着Mo含量的增加,硬度先升高后降低,断裂韧性降低,分别掺加10wt%Mo和5wt%Mo时获得最大的硬度和断裂韧性。随着热震温度的升高和热循环次数的增加,金属陶瓷中的裂纹增多;钼含量较低的Ti(C,N)金属陶瓷抗热震性能较好,当钼含量为15wt%时,压痕裂纹扩展较明显。     

Ti(C,N)基金属陶瓷氮化处理后的表面组织结构及形成机理

对Ti(C，N)基金属陶瓷进行了表面氮化处理。用SEM，EPMA，TEM／EDX分析了材料表面显微组织的特征。研究发现，材料表面形成了富N、富Ti的相，它们包覆在硬质颗粒的表面。硬质颗粒周围的环形相的体积分数大大减少。晶粒尺寸也明显减小。紧邻表面硬化层，出现了一层金属粘接相含量较高的过渡层。表面氮化处理使Ti(C，N)基金属陶瓷的表面硬度得到明显的提高，而基本上不影响其抗弯强度。表面较高的-N的活度是促使各合金元素扩散，形成上述特征组织的驱动力。     

合金组分对金属陶瓷覆层材料性能影响的研究

以Mo粉、FeB合金粉和Fe粉为基本原料，分别加入C，Cr，Ni或同时加入C，Cr，Ni合金元素成分，采用原位反应真空液相烧结工艺，在Q235钢基体上，制备三元硼化物基金属陶瓷覆层材料。研究了合金组分对覆层材料抗弯强度的影响以及对覆层硬度和耐磨性的影响。研究结果表明：在三元硼化物基金属陶瓷覆层中同时加入5％Cr，2％Ni，0．8％C作为合金组分是覆层的最佳组成，此时覆层材料具有高的抗弯强度，覆层的硬度和耐磨性指标优异。     

不同含量Ce对Ti(C,N)基金属陶瓷的结构和性能的影响

采用固溶型Ti(C,N)、Mo2C、WC、Co、Ni、Ce作为原料粉末,通过粉末冶金真空液相烧结Ce改性的Ti(C,N)基金属陶瓷材料,并对金属陶瓷复合材料的微观形貌和性能进行分析。研究结果表明,添加稀土Ce后,Ti(C,N)基金属陶瓷的硬质相变得细小且均匀,微观组织中的空隙和缺陷也减少了;随着Ce含量的增加,金属陶瓷材料的维氏硬度、抗弯强度以及断裂韧性均呈现出先增大后逐渐减小的趋势,当Ce的含量增加到0.5 wt%时,金属陶瓷材料的维氏硬度、抗弯强度以及断裂韧性达到最佳,分别为102.3 HRA、902.2 MPa、11.5 MPa·m1/2。     

超纯高铬铁素体不锈钢的性能及在隔膜法制碱装置上的应用

一、前言超纯高铬铁素体不锈钢是近十几年发展起来的一类新型不锈钢。它是用特殊方法冶炼的碳、氮等间隙元素含量极低(C N<150PPm)含26—30％Cr,1—5％Mo的Fe—Cr—Mo钢。这类钢在多种腐蚀环境中具有优良的耐蚀性(特别是抗应力腐蚀破裂性能)和抗高温氧化性能;具有良好的室温延性和缺口韧性;具有良好的可焊性。并且易于成型制作,因而是一类用途广泛,价格低廉的耐腐蚀结构材料。     

电热爆炸超高速喷涂原位合成碳化钼陶瓷涂层的实验研究

利用电热爆炸超高速喷涂技术在45#钢基体上原位合成碳化钼陶瓷涂层试样,利用X衍射(XRD)、扫描电镜(SEM)、能谱仪(EDS)和显微硬度计对涂层的成分、显微组织和显微硬度进行了分析.结果显示涂层组织致密,空隙率低,没有分层现象,涂层和基体之间形成了冶金结合.XRD显示涂层中主要是原位合成的Mo2C、MoC和.Mo相,没有氧化物的生成.涂层中形成的碳化钼陶瓷相,具有弥散强化的作用,提高了涂层的硬度.     

几种钻具材料性能及显微特征研究

本文通过金相分析、电子扫描显微分析及透射电子扫描分析,深入研究此三种材料的显微组织特征,从而找出导致三种材料性能差异的根源。最后通过理论分析和研究,讨论了造成三种钻具材料显微组织特征不同的成分因素和热处理因素。文章表明,三种材料由于其化学成分中的C、Cr、Mo元素的不同,从而在热处理过程中导致碳化物形貌、马氏体片层粗细等不同。     

Microstructure and mechanical properties of TiC0.7N0.3-HfC cermet tool materials

TiC_0.7N_0.3-HfC cermet tool materials were fabricated by hot-press sintering. Effects of different metal additives (Ni, Co, Ni-Co and Ni-Mo), sintering temperature and holding time on the microstructures and mechanical properties of TiC_0.7N_0.3-HfC cermets were investigated. Results showed that Ni-Mo or Ni-Co as metal additives was better for the mechanical properties of TiC_0.7N_0.3-HfC cermets than only Ni or only Co as the metal additives and Ni-Mo better than Ni-Co. HfC particle dispersion existed in these four cermets and only in the TiC_0.7N_0.3-HfC-Ni-Mo cermet the core-rim structure obviously existed. TiC_0.7N_0.3-HfC-Ni-Mo cermet had significantly smaller grains than the other three cermets because Ni-Mo can significantly refine the grain. With the sintering temperature increasing from 1450?°C to 1650?°C, grains grew gradually; Vickers hardness and flexural strength decreased gradually and the fracture toughness increased firstly and then decreased. With the holding time increasing from 15?min to 60?min, grains grew gradually; Vickers hardness, flexural strength and the fracture toughness increased firstly and then decreased. TiC_0.7N_0.3-HfC-Ni-Mo cermets sintered at 1450?°C with 30?min holding time had the better comprehensive mechanical properties with flexural strength of 1346.41?±?31?MPa, fracture toughness of 8.46?±?0.23?MPa?m^1/2 and Vickers hardness of 22.91?±?0.22?GPa.     

Preparation of Ni–Mo–C/Ti(C,N) coated powders and its influence on the microstructure and mechanical properties of Ti(C,N)-based cermets

Ni–Mo–C/Ti(C,N) coated powders, namely Ni–Mo alloy and Mo₂C coated Ti(C,N) composite powders, were synthesized by using a heterogeneous precipitation and thermal reduction method, then pressed and vacuum sintered to fabricate cermets. The chemical composition, microstructure and phases of the composite powders and the microstructure and properties of sintered cermets were experimentally investigated. The results show that a fine and uniform microstructure of (Ti,Mo)(C,N)-Ni cermets without the conventional core-rim structure is obtained. The phases formed during the preparation of the coated powders as well as the cermets were analyzed by means of a X-ray diffraction (XRD) technique. The XRD result confirms the formation of the Ni₃Ti phase in the cermets. Due to the formation of the non-magnetic Ni₃Ti and the dissolution of Mo in Ni binder phase, the magnetic properties are strongly retarded. The fracture of the cermets is mainly characterized by inter-granular and dimple fractures. Better mechanical properties can be obtained in comparison with conventionally fabricated ones.     

Effects of TiC/TiN addition on the microstructure and mechanical properties of ultra-fine grade Ti (C, N)–Ni cermets

Two series of Ti (C, N)-based cermets, one with TiC addition and the other with TiN addition, were fabricated by conventional powder metallurgy technique. The initial powder particle size of the main hard phase components (Ti (C, N), TiC and TiN) was nano/submicron-sized, in order to achieve an ultra-fine grade final microstructure. The TiC and TiN addition can improve the mechanical properties of Ti (C, N)-based cermets to some degree. Ultra-fine grade Ti (C, N)-based cermets present a typical core/rim (black core and grayish rim) as well as a new kind of bright core and grayish rim structure. The average metallic constituent of this bright core is determined to be 62 at% Ti, 25 at% Mo, and 13 at% W by SEM–EDX. The bright core structure is believed to be formed during the solid state sintering stage, as extremely small Ti (C, N)/TiC/TiN particles are completely consumed by surrounding large WC and Mo₂C particles. Low carbon activity in the binder phase will result in the formation (Ni₂Mo₂W)C_x intermetallic phase, and the presence of this phase plays a very important role in determining the mechanical properties of TiN addition cermets.     

Improvement of microstructure,mechanical properties and cutting performance of Ti(C,N)-based cermets by ultrafine La2O3 additions

Ti(C,N)-WC-Mo₂C-TaC-Co-Ni cermets with various content of La₂O₃ were prepared by gas-pressure sintering at 1450 °C. The effects of ultrafine La₂O₃ additions (0, 0.05, 0.1 and 0.2 wt%) on the microstructure, mechanical properties, wear resistance and cutting performance of cermets were explored. In the microstructure of cermets, the La₂O₃ particles and dissolved La element in binder phases were observed, which could inhibit the dissolution-precipitation process of ceramics phases during liquid-sintering. Furthermore, the La₂O₃ could absorb and react with the impurity Al element with low melting point from raw powders, avoiding the appearance of liquid phase at the low temperature and partial overheating during sintering process. These mechanisms could inhibit the abnormal growth of Ti(C,N) core-(Ti,W,Mo,Ta)(C,N) rim structures effectively, leading to the thinning of brittle rim phases and coarsening of wear-proof Ti(C,N) particles. The decrease of proportion of brittle rim phase and ultrafine Ti(C,N) particles promoted the fracture toughness. The increase of proportion and grain size of Ti(C,N) improved the hardness, wear resistance and cutting performance significantly. However, the excessive addition of La₂O₃ would result in the agglomeration of La₂O₃, causing the sharp decline of mechanical properties and cutting performance. The cermet with 0.1 wt% La₂O₃ addition possessed the optimal mechanical properties with Vickers hardness, transverse rupture strength and fracture toughness of 1710 (HV30) Kgf/mm², 2480 MPa and 11.7 MPa m^1/2, respectively.     

Fabrication of Ti(C,N)‐based cermets by in situ carbothermal reduction of MoO3 and subsequent liquid sintering

Ti(C,N)‐based cermets were fabricated by in situ carbothermal reduction of MoO₃ and subsequent liquid sintering in a single heating process. The densification behavior, phase formation, and microstructure evolution of the cermets were characterized by DSC, XRD, SEM, and TEM. The results showed that near‐fully dense Ti(C,N)‐based cermets with fine carbonitride grains could be obtained by the above‐mentioned method. The carbonitride grains of the cermets still exhibited typical core/rim structures and evenly distributed in the binder phase, but the rim phase was more complete and thinner compared with traditional cermets. In addition, the interfaces between the ceramic phase and binder phase of the cermets were atomically smooth, having the orientation relationship of ()_R//(110)_B with a perfect coherency state. The prepared Ti(C,N)‐based cermets produced with MoO₃ showed excellent comprehensive mechanical properties having a transverse rupture strength of 2461±62 MPa, a Rockwell hardness of 88.0±0.1 HRA, and a fracture toughness of 22.3±0.4 MPa·m^1/2, respectively.     

Microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in situ carbothermal reduction of TiO2 and subsequent liquid phase sintering

Ti(C,N)-based cermets were prepared by in situ carbothermal reduction of TiO₂ and subsequent liquid phase sintering in one single process in vacuum. The densification behavior, phase transformation, and microstructure evolution of the cermets were investigated by DSC, XRD, SEM, and EDX. The results showed that the carbothermal reduction of TiO₂ was completed below 1250 °C, and Ti(C,N)-based cermets with refined grains were obtained after sintered at 1400 °C for 1 h by this method. The hard phase of the cermets mainly exhibited white core/gray rim structure, in great contrast to the typical black core/gray rim structure of hard phase in traditional cermets. Ti(C,N)-based cermets prepared by this novel method showed excellent mechanical properties with a transverse rupture strength of 2516±55 MPa, a Rockwell hardness of 88.6±0.1 HRA, and a fracture toughness of 18.4±0.7 MPa m^1/2, respectively.     

Evolution of microstructure and interfacial characteristics of complete solid-solution Ti(C,N)-based cermets fabricated by mechanical activation and subsequent in situ carbothermal reduction

Complete solid-solution Ti(C,N)-based cermet, with no typical core-rim structure, was synthesized through mechanical activation and subsequent in situ carbothermal reduction method. XRD, SEM, TEM, and C/N analysis were used to investigate the microstructure, phase transformation, and the interfacial characteristics of the present cermets. During solid-state sintering, the (Ti,Mo)C/(Ti,Mo)(C,N) phases formed through the transformation of Mo-based solid solution which generated by mechanical activation. Then, the formed (Ti,Mo)C/(Ti,Mo)(C,N) continuously dissolved into the nickel-based binder above 1100 °C. It was found that in the subsequent stage of liquid sintering, the mechanical activation and also the presence of extremely fine TiC/Ti(C,N) particles accelerated the Mo diffusion into the hard phase, resulting in a large quantity of (Ti,Mo)(C,N) solid solutions formed in the nickel-based binder. Finally, complete (Ti,Mo)(C,N) solid-solution phase was obtained via dissolution and re-precipitation. The higher toughness and transverse rupture strength (TRS) of the synthesized new cermet, as compared with traditional cermets, were mainly caused by the increased crack deflection and transgranular fracture of the novel cermets. Moreover, the interface among the Ni-based binder phase and complete solid solution hard phase exhibited a semi-coherency state with high-density dislocations, which also significantly improved the TRS and toughness of the synthesized cermets.     

Effects of (Ta0.2W0.2Nb0.2Mo0.2V0.2)C high-entropy carbide content on the microstructure and properties of Ti(C0.7N0.3)-based cermet

Using pre-synthesized high-entropy (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C carbide as the reinforcing phase, Ti(C_0.7N_0.3)-based cermets were prepared by pressureless sintering at 1600 °C. The results revealed that due to the solid solution reaction between the mono-carbide and (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C, only one set of face-centered-cubic diffraction peaks in XRD was detected in the as-sintered cermets, alongside the typical core-rim structure. Compared to the Ti(C_0.7N_0.3)-based cermets without high-entropy reinforcing phase, the Vickers hardness was increased from 17.06 ± 0.09 GPa to 18.42 ± 0.33 GPa and the fracture toughness was increased from 9.21 ± 0.31 MPa m^1/2 to 12.56 ± 0.23 MPa m^1/2 by adding 10 wt% (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C. The wear resistance of the cermet was enhanced significantly with increasing (Ta_0.2W_0.2Nb_0.2Mo_0.2V_0.2)C content. This work provided a potential that the high-entropy carbide can be applied as an effective reinforcing phase in the preparation of high-performance Ti(C_0.7N_0.3)-based cermets.     

Effect of Mo addition mode on the microstructure and mechanical properties of TiC–high Mn steel cermets

In TiC- and Ti(C,N)-based cermets, the wettability of the ceramic phase with the metallic binder is commonly increased through supplementation with Mo in the form of pure Mo powder or Mo₂C. Herein, TiC–high Mn steel cermets were fabricated by conventional powder metallurgy techniques using Fe–Mo pre-alloyed powders as binders to guarantee uniform Mo distribution, and the cermet preparation process was optimized and investigated in detail. The microstructures of the thus obtained cermets were observed by scanning electron microscopy and compared to those of a Mo-free cermet and a cermet prepared using pure Mo powder. The grain size of Fe–Mo powder cermets exceeded that of the Mo-free cermet but was much smaller and more homogeneous than that of the Mo powder cermet. For Fe–Mo powder cermets, angular and tetragonal TiC particles were observed at Mo contents of <1.2 wt%, while round shapes became dominant at higher Mo contents. The hardness of Fe–Mo powder cermets increased with increasing Mo content, as did transverse rupture strength, which was maximal (2264 MPa) at a Mo content of 2.4 wt%, while impact toughness was maximal (11.2 J/cm²) at a Mo content of 1.2 wt%. The above values exceeded those reported for similar conventional cermets, and the use of Fe–Mo pre-alloyed powder as a metallic binder was therefore concluded to be an attractive strategy of increasing the strength and toughness of TiC–high Mn steel cermets.