Effect of WC-Co granules on mechanical properties and microstructure of Ti(C,N)-based cermets

The effect of WC-Co granules addition on the microstructure and mechanical properties of TiC(nm)-TiN(nm)-Co-Mo-C cermets (shown as Ti(C,N)-based cermets in other part of the paper) was studied in this paper. The results show that the WC-Co granules distribute homogeneously in the matrix of Ti(C,N) based cermets. There was a transitional layer containing intermetallic compound between the WC-Co granules and the matrix of Ti(C,N) based cermets. Transverse rupture strength(TRS) and fracture toughness increase with the increase of WC-Co granules, reach a peak value at 15 vol% addition in comparing with that of without WC-Co granules addition. The toughening mechanisms were crack deflection, branching and trapping. However, when the content of WC-Co granules was higher than 15 vol%, the excessive content of WC-Co granules leaded to voids in the cermets, which decreased the mechanical properties of the cermets.     

Effect of carbon content on the microstructure and mechanical properties of Ti(C, N)-based cermets

Three series of Ti(C, N)-based cermets with various carbon content were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). Hardness (HV) and transverse rupture strength (TRS) were also measured. A lower carbon content resulted in the aggregation of ceramic grains because the absorbed oxygen of the powder mixture could not be outgassed completely, and then the ceramic grains could not be well-wetted by liquid metal during sintering. On the contrary, too high carbon content resulted in the formation of graphite phase. An increased carbon content decreased the dissolution of tungsten, titanium and molybdenum in the binder phase. The volume fraction of the binder is not much influenced by the carbon content. The highest hardness and TRS were found for the cermet with 1.5 wt.% carbon addition, which was characterized by fine grains and moderate thickness of rim phase.     

Influence of ZrC addition on the microstructure,mechanical properties and oxidation resistance of Ti(C,N)-based cermets

In this study, Ti(C,N)-WC-NbC-ZrC-Co-Ni cermets were prepared by sintering-hip at 1450?°C. The effect of ZrC addition on the microstructure, mechanical properties, oxidation resistance and wear resistance of Ti(C,N)-WC-NbC-Co-Ni cermets were explored in detail. The results show that ZrC addition plays the role of inhibitor in the dissolution–reprecipitation process, which can increase the wear-resistant carbide phases and inhibit the precipitation of brittle (Ti,W,Nb)(C,N) rim phase. Therefore, the core-rim structures are refined and the Nb content in binder increases, which enhance mechanical properties and oxidation resistance of cermets. With the increasing ZrC content, the oxidation resistance of cermets can be improved constantly, while the transverse rupture strength, fracture toughness and wear resistance of these cermets increase first and then decrease. The cermet with 1?wt% ZrC exhibits the transverse rupture strength of 2549?MPa and highest fracture toughness of 13.0?MPa?m^1/2. The oxidation weight gain of cermets containing 5?wt% ZrC after holding 100?h at 750?°C in air is 2.8?×?10^?6 g?mm^?2, which is only 22% of that in the cermets without ZrC addition.     

Ti(C,N)-based cermets containing uniformly dispersed ultrafine rimless grains: Effect of VC additions on the microstructure and mechanical properties

Difference in lattice parameters and physical properties of core-rim structure leads to mismatch at the core-rim interfaces. In this respect, VC was adopted to shrink the lattice of rims and intended to reduce the lattice misfit. Small amount of VC (0.8 wt%) effectively decreased the grain size from 0.77 μm to 0.57 μm, with an increased lattice parameter of the core-rim phase. Higher VC content accelerated the dissolution and precipitation process, resulting in the formation of thicker rims and smaller lattice parameters of core-rim structure. The same lattice parameters of core-rim phases were achieved with 4.8 wt% of VC addition. A distortion zone with a thickness of 3–5 atomic layers was confirmed, which located at the boundary of binder and gray rim. VC induced the formation of spherical rimless grains, which were uniformly dispersed in the binder and usually attached to the coarse core-rim grains. Black ultrafine rimless grains exhibited larger lattice parameters than Ti(C,N) cores due to the increased C/N ratios. Ti(C,N)-based cermets with uniformly dispersed rimless grains were achieved, which showed effectively improved the bending strength of cermets, with in-situ formed dimples inside the binders during the fracture.     

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.     

Submicron Ti(C,N)-based cermets with improved microstructure using high-energy milled and subsequent heat-treated ultrafine Ti(C,N) powders

Ti(C,N)-based cermets with ultrafine or submicron black core-rim grains are attracting candidates for high-quality tools and dies, due to their high hardness and strength. However, high chemical activity of ultrafine Ti(C,N) powders lead to the increased instability and difficulty to control the sintering process, since the denitrification and interface diffusion are accelerated during the solid-state reaction. Based on this, owing to the unrealized commercial ultrafine-grade powders, ultrafine Ti(C,N) powders with an average grain size around 150 nm, low oxygen content and few dislocations are fabricated via the high-energy ball milling and subsequent heat treatment of commercial micron Ti(C,N) powders. Related morphology evolution, microstructure and composition of the ultrafine Ti(C,N) powders are investigated. Dense submicron Ti(C,N)-based cermets with grain size of 0.62 μm and uniform core-rim phases are successfully prepared by using the as-fabricated ultrafine Ti(C,N) powders. Compared to cermets via the conventional high-energy milling route, submicron Ti(C,N)-based cermets exhibit higher hardness of 1750 ± 40 N/mm², bending strength of 1960 ± 135 MPa, and satisfactory fracture toughness of 9.2 MPa m^1/2, owing to smaller grain size, uniform microstructure and partial black core-rim grains.     

Strengthened Ti(C,N)-based cermets using high-energy ball-milled NiTiC binders: Microstructure and mechanical properties

High-energy ball-milled NiTiC powders were used for preparing Ti(C, N)-based cermets. Effect of NiTiC content on the morphology, composition, interface structure and mechanical properties of cermets were investigated. NiTiC binders promoted the formation of inner rims on Ti(C, N) cores and hindered their coalescence, leading to well-distributed microstructure. Binder had little effect on the composition of rims, but greatly affected the interface structure of core-rim and rim-binder. Complete inner rim could decrease the lattice mismatch between outer rim and core, forming highly coherent interface. With increasing the Ti-C in Ni, the rim-binder boundaries evolved from semi-coherent to coherent interface, due to the decreased lattice mismatch. Small difference in Vickers hardness of cermets was found, with the values ranging from 1622 to 1684 N/mm². Bending strength of cermets increased from 1330 to 2073?MPa, with the Ti-C content from 0 to 20?wt%. Further increasing the Ti-C could lead to thick rims, resulting in decreased strength and toughness. This work showed us a way to strengthen the Ti(C, N)-based cermets via modifying the interface structure.     

Effects of metal phases on microstructure and mechanical properties of microwave-sintered Ti(C,N)-based cermet tool

A kind of Ti(C, N)-based cermet tool material was prepared by microwave sintering. The influence of metal phases (Ni, Co, and Mo) on densification and mechanical properties was studied by orthogonal test. The results indicated that Co was more significant in improving relative density and fracture toughness than Ni, while Ni and Co had the similar effects on increasing the hardness of Ti(C, N)-based cermet. Mo can improve fracture toughness but decrease hardness. Ti(C, N)-based cermet with 6 wt% Ni, 6 wt% Co and 6 wt% Mo (TN6C6M6) had the optimal comprehensive mechanical performances, and its fracture toughness and hardness were better than that of Ti(C, N)-based cermet prepared by conventional sintering. The increasing of sintering temperature promoted the uniformity of microstructure and significantly improved densification and hardness of the Ti(C, N)-based cermet. The highest fracture toughness of TN6C6M6 (12.41 ± 0.33 MPa·m^1/2) was achieved when sintered at 1600°C. For the microwave-sintered Ti(C, N)-based cermet, heat preservation period had little effect on densification. The relative density can reach up to 98.6% even though the heat preservation period was 0 minute.     

Effect of diamond addition on microstructure and mechanical properties of Ti(C,N)-based cermets

This study explored the effect of diamond content (0, 0.3, 0.6, and 0.9 wt%) onTi(C_0.5,N_0.5)-based cermets prepared via vacuum sintering with respect to their final mechanical properties and microstructures, characterized using X-ray diffractionand scanning electron microscopy. After liquid phase sintering, all cermets exhibited a ‘black core/grey rim'and partial ‘white core/grey rim'structure. The cermet with 0.6 wt% diamond exhibited optimal mechanical properties with a Vickers hardness of 1795 ± 32 H V, transverse rupture strength of 2026 ± 45 MPa, and plane strain fracture toughness of 12.95 ± 0.3 MPa m^1/2. This is due to grain refinement and the uniformly distributed ‘white core/grey rim'grains. During the incipient liquid formation stage,a higher carbon activity arising due to diamond graphitization may shift the equilibrium towards the product, thereby yielding additional white cores due to the consumption of heavy elements in the binder. Excessive diamond introduction inhibited the dissolution of Ti(C_0.5,N_0.5) into the binder, resulting in fewer white cores.     

Structure and properties of PVD TiAlN and TiAlN/CrAlN coated Ti(C,N)-based cermets

Ti(C, N)-based cermets were coated with TiAlN and TiAlN/CrAlN films by physical vapor deposition. The cross-sectional morphology was characterized by scanning electron microscopy (SEM), and the adhesive strength was evaluated by the scratch test. Cutting tests on the coated cermets were conducted on the different cutting conditions. The cutting performance and wear mechanism were analyzed with SEM and EDS. It is found that TiAlN coating has a better adhesion to the cermet substrate. The coated cermet inserts show better wear resistance than the uncoated ones. By contrast, the TiAlN coating suffers a slight abrasive flank wear. However, the TiAlN/CrAlN coating show more severe adhesive flank wear because of the Cr interdiffusion between the inserts and the workpiece. In addition, TiAlN coating is weak in resisting against oxidation wear, while the TiAlN/CrAlN coating has an excellent resistance to oxidation.     

Nanostructure and bimodal structure of Si3N4 ceramics developed by spark plasma sintering method

Abstract

The densification of high energy ball milled Si₃N₄ nanopowders through spark plasma sintering was investigated. Nanoceramics of Si₃N₄, with fine microstructure, comprising of grains with a diameter of ～70 nm, were produced after sintering at 1600°C for 5 min in N₂ atmosphere with a fast heating rate of 300 K min^?1. The size and the aspect ratio of Si₃N₄ grains increased with decreasing heating rate and increasing holding time and temperature. Post-annealing of sintered ceramics at 1850°C for 3 h favoured development of a self-reinforced bimodal microstructure containing large elongated grains.     

碳氮化钛对低碳镁碳砖性能的影响

研究了碳氮化钛加入到低碳镁碳砖中对其性能的影响,并采用XRD物相分析、SEM显微分析研究了碳氮化钛对低碳镁碳砖基质部分烧后性能的影响。结果表明:镁碳砖基质部分经1600℃3h埋炭处理后,碳氮化钛仍均匀分布在基质中,并和MgO发生一定程度的固溶;加有碳氮化钛的镁碳砖经1600℃3h埋炭处理后,体积密度有所降低,气孔率升高,线膨胀率增大,常温耐压强度有所减小;碳氮化钛对镁碳材料的抗氧化性有所改善,但不及传统的金属铝粉;材料同样表现出良好的抗渣性。     

Improvement in microstructure and mechanical properties of Ti(C,N) cermet prepared by two-step spark plasma sintering

A fine grained Ti(C, N) cermet tool material was prepared by two-step spark plasma sintering. Microstructure evolution and densification mechanisms of Ti(C, N) during spark plasma sintering were studied. Effect of two-step sintering process and Ni content on microstructure and mechanical properties were also investigated. The critical activated densification temperature of Ti(C, N) is about 1300?℃, and the rapidest densification rate takes place at 1300?℃~1400?℃. Grains are in the size of 1?µm when the Ti(C, N) cermet was prepared by two-step spark plasma sintering. The optimal flexural strength, fracture toughness and Vickers hardness are 1094?±?42?MPa, 7.2?±?0.5?MPa?m^1/2 and 18.3?±?0.4?GPa, respectively. The Ti(C, N) cermets containing more content of Ni have higher toughness, which is due to the remarkable toughening effect of crack bridging by large grains.     

Carburization and wear behavior of self-lubricating Ti(C,N)-based cermets with various secondary carbides

Self-lubricating Ti(C,N)-based cermets were manufactured using vacuum sintering and solid carburizing in this study, and the effects of various carbides on the carburization and wear behavior of the cermets were investigated. The findings demonstrate that solid carburizing resulted in strong graphite precipitation in all the Ti(C,N)-based matrices. Refractory carbides significantly affect the morphological characteristics of graphite in cermets. The activated carbon atoms in the cermet matrix are consumed in two ways: rearrangement followed by precipitation in the form of graphite and combination with metal atoms followed by precipitation in the form of carbides or carbonitrides. As the amount of refractory carbide dissolved in the binder phase increases, more carbon atoms are consumed by bonding with metal atoms, and less graphite is precipitated. The precipitation of carbides and carbonitrides in the ceramic phase increases the rim phase thickness. After carburization, the mechanical properties of the cermets were noticeably degraded owing to the introduction of graphite and the coarsening of ceramic particles. However, the presence of graphite significantly reduced the friction coefficient of the cermet material owing to its good lubrication effect. The decreased mass loss and better wear morphology suggest that the wear deterioration of all the cermets is remarkably mitigated by carburization. The wear properties of cermets are determined by the mechanical properties and the lubrication conditions of the contact surfaces, and good lubrication conditions can partially compensate for the degradation of the mechanical properties of cermets in the sliding wear process.     

Ti(C,N)-based cermets with strengthened interfaces: Roles of secondary cubic carbides

Core-rim structure, concerning its interface structure and internal stress, plays an important role in mechanical performance of Ti(C,N)-based cermets. Four types of cermets containing equimolar TaC, VC, ZrC, and NbC were fabricated, in order to reveal the synergetic relationship between core-rim structure and mechanical properties. VC and ZrC effectively inhibited the grain growth, while TaC and NbC favored for coarser core-rim grains. A thin distortion layer at the rim-binder interface was confirmed, formed during the solidifying stage. Compared to the TaC, ZrC and NbC, VC shrunk the lattice parameters of rims and effectively decreased the lattice misfit of the distortion zone from around 4.0%-0.8%. Cermets containing VC showed satisfactory bending strength of 2099 MPa and toughness of 10. 3 MPa m^1/2, owing to the strengthened rim-binder interface. TaC and NbC exhibited the similar roles in cermets with comparable mechanical properties, while addition of ZrC increased the lattice misfit of core-rim structure, resulting in poor mechanical performance. Decreased lattice misfit of rim-binder interface changed the fracture mode of cermets from intergranular to transgranular fracture, with in-situ formed dimples.     

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.     

Ti(C,N)对刚玉质浇注料性能的影响

骨料采用电熔白刚玉,基质采用白刚玉细粉、活性α-Al2O3微粉、SiO2微粉及Ti(C,N)微粉,按骨料与基质质量比为70:30,α-Al2O3微粉和Ti(C,N)微粉总质量分数固定为10%,制备了Ti(C,N)含量(质量分数)分别为0、5%和10%的三种刚玉质浇注料,对比了三种材料的常温物理性能、抗碱(K2O)性能及抗渣性能,并借助XRD和光学显微镜研究了材料的物相组成和显微结构。结果表明:加入Ti(C,N)后,刚玉质浇注料经1500℃3h热处理后强度显著增大,抗碱(K2O)性能及抗渣性能随Ti(C,N)加入量的增加而逐渐提高。其主要机理为:Ti(C,N)促进了材料的高温烧结,改善了材料的显微结构;同时Ti(C,N)化学稳定性优良,难于被熔渣润湿,材料基质中均匀分散的Ti(C,N)减弱了碱(K2O)及熔渣对刚玉质浇注料的渗透和侵蚀。     

Microstructural evolution and phase transition mechanism of Ti(C,N)-based cermets during vacuum sintering process

Ti(C,N)-based cermets were fabricated using section vacuum sintering. The density and shrinkage ratio of sintered samples were recorded and analyzed. Phase transition, microstructure and interface behaviors of cermets were examined by transmission electron microscope, X-ray diffractometer and scanning electron microscope. As the sintering temperature rising, the number of pores in cermets was decreased and the density of samples was increased. Moreover, with the progress of sintering, atoms of various elements were constantly diffusing and gathering, affecting the formation of different microstructure, and the angle and intensity of each XRD peak were also constantly changing slightly, or disappearing at a certain temperature. These relevant results indicated that the proportion of heavy element to Ti in the hard phase would affect its lattice parameter. After the appearance of liquid phase, the densification mechanism changed from surface diffusion to grain boundary diffusion, thus accelerating the densification. With the proceeding of sintering process, various microstructures were formed such as core - rim/rimless structure. Finally, the process of interface change in core rimless phase transition was discussed. This rim phase, formed in solid state sintering process while failing to develop into core-rim structure after liquid sintering, was formed by some heavy elements short-range diffusion into core phase. The orientation different and the misfit between this core and rim were relatively large. While after liquid sintering, the semi-coherency or even coherency state at the interface of core-rimless and binder was formed.     

Ti(C,N)基金属陶瓷的显微结构和力学性能研究

采用真空热压烧结工艺制备三种不同掺杂的Ti（C,N）基金属陶瓷。借助于SEM分析了其显微结构,并测试了其力学性能和相对密度。实验结果表明：配方41.2wt%TiC-10wt%TiN-14wt%（Ni＋Co）-12wt%Mo2C-15wt%WC-6wt%TaC-0.8wt%Cr2C3-1wt%C的金属陶瓷综合性能最好,晶粒较细、均匀,具有明显的黑芯-灰壳结构;气孔较少,致密度较高。断裂机理主要是沿晶断裂,部分为混合型断裂（穿晶断裂和沿晶断裂）。金属相存在着明显的撕裂棱。其维氏硬度为12.5GPa,断裂韧性为8.9MPa·m1/2,抗弯强度为1286MPa,相对密度达到了99.2%。     

Ti(C,N)基金属陶瓷的研究进展

介绍了Ti（C，N）基金属陶瓷的基本组成和结构，综述了Ti（C，N）基金属陶瓷的研究现状，指出了未来的发展方向和应用。