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.     

Insight into tribological and corrosion behaviour of binderless TiCxNy ceramic composites processed via pulsed electric current sintering technique

The study presents the corrosion behaviour and wear response of pulsed electric current sintered binderless TiC₅₀N₅₀, TiC₇₀N₃₀, and TiC₉₀N₁₀ based ceramic composites, consolidated by spark plasma sintering (SPS), and the relative densities were evaluated using the Archimedes principle. The microstructural evolutions of the sintered samples were examined through various microscopy techniques, and their susceptibility to corrosion in aggressive chloride environment was assessed using open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The microstructural examination of the specimens showed the presence of different phases within the titanium carbonitride (TiCN) cermets. The wear resistance evaluated using the frictional coefficient (COF) and calculated wear rate showed that the specimens exhibited an improved resistance. The specimens further showed enhanced resistance to corrosion in the test electrolyte, as the TiC₅₀N₅₀ cermet displayed enhanced resistance to the aggressive chloride ions in comparison to the other specimens.     

Preparation and toughening mechanism of Mo2NiB2-based cermets with SiC whiskers

Mo₂NiB₂ is a kind of cermet with excellent mechanical properties, stable chemical properties, and excellent corrosion resistance and is often used in wear-resistant application fields, such as injection molding machine parts, can making tools and hot copper extruding dies. The brittleness of Mo₂NiB₂-based cermets limits their wide application. Mo₂NiB₂-based cermets were prepared by the vacuum sintering method, the effect of SiC whiskers (SiCw) on the microstructure and mechanical properties of cermets was investigated, and the toughening mechanism of SiCw on cermets was further discussed. The results indicate that with increasing SiCw content, the indentation fracture toughness (K_IC), transverse fracture strength (TRS), and Vickers hardness (HV) of the cermets first increase and then decrease. The HV, TRS, and indentation fracture toughness of Mo₂NiB₂-based cermets with 0.5 wt% SiCw are 1 113 HV, 1 620 MPa, and 27.97 MPa·m^1/2, respectively, which are 16.8%, 22.7%, and 25% higher than those without SiCw. In the sliding friction tests, Mo₂NiB₂-based cermets with 0.5 wt% SiCw have the smallest friction coefficient, low wear rate, and high wear resistance. SEM observation and analysis of the crack path and fracture surface showed that the toughening mechanism is whisker bridging, crack deflection, microcrack toughening, and whisker pull-out. The results indicate that the addition of 0.5 wt% SiCw can effectively improve the mechanical properties of Mo₂NiB₂-based cermets and further expand the application space of Mo₂NiB₂-based cermets.     

反应硼化烧结WCoB基金属陶瓷的组织与性能

采用单质钨粉、钴粉和硼粉结合反应硼化烧结法制备了WCoB基金属陶瓷,研究了WCoB基金属陶瓷在烧结过程中的物相转变和尺寸变化,烧结温度对其力学性能和显微组织的影响。结果发现:随着烧结温度的升高,材料物相逐渐由单质相变为二元硼化物相和三元硼化物相,并且材料的尺寸先发生细微收缩,再在硼化反应过程中逐渐增加,最后在液相烧结过程中逐渐减小;随着烧结温度的升高,WCoB基金属陶瓷的抗弯强度和硬度先增加后减小,在1420℃达到最大,分别为1470 MPa和84.6HRA,显著提高了WCoB基金属陶瓷的抗弯强度。     

FeWB基陶瓷在真空烧结过程中的组织和相转变

研究了烧结温度和保温时间对反应硼化烧结制备FeWB基陶瓷的影响。利用X射线衍射,扫描电镜和能谱仪对FeWB基烧结过程中的相转变,微观组织以及反应机理进行了表征。结果表明FeWB硬质相是通过W + Fe2B = FeWB + Fe和FeB + W = FeWB两种方式合成的,并且反应生成的FeWB晶粒呈各向异性分布。在温度区间为800℃-1150℃之间,FeWB基陶瓷的密度骤然升高,这与Fe2B相的熔化有关。在1300℃时,由于W2B相的存在,会使FeWB相转变为Fe7W6相,从而使密度进一步升高。随着烧结温度的提高,通过液相烧结制备的金属陶瓷表现出相对均匀的微观结构,而且原位合成的FeWB颗粒会发生长大。为了获得较高的致密度,实验结果表明,FeWB基陶瓷的烧结温度应控制在1150℃-1250℃之间。其次,适当的增加铁和硼铁的含量有利于烧结的致密化。     

Ti(C,N)-based cermets with fine grains and uniformly dispersed binders: Effect of the Ni–Co based binders

Metallic binder is a key factor affecting the microstructure and mechanical properties of Ti(C,N)-based cermets. To optimize the overall performances, cermets with various weight ratios of Ni/(Co + Ni) ranging from 0 to 1 were fabricated by gas pressure sintering. Microstructure, phase formation, interface structure and related mechanical properties of the sintered cermets were investigated. With the increase of the Ni/(Co + Ni) ratios, the black cores became smaller and grains of Ti(C,N) dispersed uniformly. Compared to the pure Ni or Co, Ni–Co binders accelerated the formation of rim phases, and avoided the nonuniform dispersed binder pools. When the ratio was 0.5, the cermets showed fine grains, uniformly dispersed binders and small lattice misfit of the core-rim interface, exhibiting the optimal mechanical properties, i.e. satisfactory Vickers hardness of 1670 (HV30) Kgf/mm², bending strength of 1970 MPa and Fracture toughness of 8.94 MPa m^0.5. This work sheds light on constructing the relationship between the microstructure, mechanical performance of Ti(C,N)-based cermets and the Ni/Co-based binders.     

包裹型SiO2/Al复合粉体的制备及烧结性能研究

为了克服金属陶瓷两相分布不均、界面不润湿和难以烧结致密等难题,采用球磨技术将增强相均匀包裹在基体材料表面,研究包裹型SiO₂/Al复合粉体的球磨制备工艺及其烧结性能,提高金属陶瓷的综合性能。结果表明,随着球磨时间的延长,SiO₂/Al复合粉体的比表面积先增大后减小,球磨6 h获得的复合粉体比表面积最大,达到8.1 m2·g?1。随着球料比的增大,SiO₂/Al复合粉体的比表面积先增大后减小,说明SiO₂包裹在Al粉表面的量呈现先增多再减少的趋势。随着球磨转速的增大,SiO₂/Al复合粉体比表面积先增大后减小。随着烧结温度的提高,SiO₂/Al金属陶瓷表面硬度先增高后降低,在烧结温度为900 ℃时,SiO₂/Al金属陶瓷的表面硬度达到最高。球磨时间为6 h,球料比为2:1,球磨转速为360 r·min?1,烧结温度900 ℃可以获得性能较佳的SiO₂/Al金属陶瓷。     

球磨时间对Ti(C0.7,N0.3)晶粒及Ti(C0.7,N0.3)基金属陶瓷组织和性能的影响

球磨是金属陶瓷制备中的关键工艺,滚动球磨是目前成本较低、在实际工业生产中应用最广泛的球磨方式。为了量化分析球磨时间对Ti（C_0.7,N_0.3）基金属陶瓷的影响,采用湿混的方法在固定的球料比、球磨机转速和球磨介质添加量的条件下,研究球磨时间因素对Ti（C_0.7,N_0.3）的晶粒尺寸、应变和晶格常数的影响,以及对烧结后的Ti（C_0.7,N_0.3）基金属陶瓷微观组织和物理力学性能如收缩率、密度、硬度和横向断裂强度的影响。结果表明,随球磨时间增加,Ti（C_0.7,N_0.3）晶粒尺寸下降,而微观应变增加。同时,Ti（C_0.7,N_0.3）的晶格常数也增加,这与晶粒微观应变增加以及少量原料的氧化加剧有关。对烧结后的微观组织而言,球磨时间的增加导致金属陶瓷硬质相平均晶粒尺寸下降,但是当球磨时间达到72和96 h的时候,金属陶瓷中出现了0.1 μm左右的孔隙,这与球磨过程中氧含量的增加导致烧结时脱气反应以及Ti（C,N）硬质相和Ni粘接剂之间的润湿性变差有关。Ti（C_0.7,N_0.3）基金属陶瓷微观组织中白芯结构数量随球磨时间的增加明显减少了,芯中Mo含量的下降而Ti含量的增加是白芯数量下降的原因。环形相随球磨时间的增加变薄了,这一现象与不同尺寸的颗粒溶解度以及颗粒的均匀性有关。另外,随着球磨时间的增加,Ti（C_0.7,N_0.3）基金属陶瓷的硬度增加,而横向断裂强度随球磨时间的增加先增加后下降,其中孔隙对横向断裂强度的损害作用要大于晶粒细化对强度提高的作用。     

(Ti,W,Mo)C-NiCo金属陶瓷刀具切削性能研究

采用等离子体烧结方法制备出了(Ti,W,Mo)C-NiCo金属陶瓷刀具。研究了制备出的金属陶瓷刀具在切削正火态45钢时的切削行为,得出了切削用量对刀具耐用度的影响规律。     

Processing of Boron Carbide-Aluminum Composites

The processing problems associated with boron carbide and the limitations of its mechanical properties can be significantly reduced when a metal phase (e.g., aluminum) is added. Lower densification temperatures and higher fracture toughness will result. Based on fundamental capillarity ther modynamics, reaction thermodynamics, and densification kinetics, we have established reliable criteria for fabricating B₄C–Al particulate composites. Because chemical reactions cannot be eliminated, it is necessary to process B₄C–AI by rapidly heating to near 1200°C (to ensure wetting) and subsequently heat-treating below 1200°C (for microstructural development).