烧结温度对(Ti,W,Mo,Nb)(C,N)-(Co,Ni)金属陶瓷组织结构和性能的影响

以(Ti,W,Mo,Nb)(C,N)-(Co,Ni)基金属陶瓷材料为研究对象,研究烧结温度对金属陶瓷的成分、微观组织和力学性能的影响,初步探讨成分、微观组织与材料强度的关系.结果 表明:烧结温度对(Ti,W,Mo,Nb)(C,N)-(Co,Ni)基金属陶瓷组织特征有显著的影响;合金的总碳含量随着烧结温度的提高而降低,当...     

Effects of Cr3C2 addition on the corrosion behavior of Ti(C,N)-based cermets

The Ti(C, N)-based cermets with different Cr₃C₂ addition were prepared and the effects of Cr₃C₂ addition on the microstructure and properties of cermets were discussed. The corrosion behavior of the cermets with different Cr₃C₂ addition was investigated emphatically in 2 mol/L HNO₃ solution. The results indicate that there is no obvious effect of Cr₃C₂ addition on the densification of the cermets, and all cermets are almost fully densified during sintering. The thickness of rim phase is reduced and the core size is increased remarkably in the cermets with 1 wt.% and 3 wt.% Cr₃C₂ addition; the grains are refined significantly in the cermets with the increase of Cr₃C₂ addition to 5 wt.%. The hardness and transverse rapture strength of the cermets are improved with Cr₃C₂ added properly. In HNO₃ solution, the corrosion resistance of cermets is improved remarkably by Cr₃C₂ addition. The corrosion of binder phase is predominant in the cermets in which the Ni binder phase without Cr has lower corrosion resistance than the rim phase; whereas the corrosion resistance of binder phase with high Cr content is better compared to the rim phase, so that the degradation of rim phase is predominant and a reticulate binder phase forms. With the increase of Cr₃C₂ addition, the Mo content in rim increases, and it is bad for the corrosion resistance of rim phase. Additionally, the inner rim phase has lower corrosion resistance than the outer rim phase owing to the higher Mo content.     

Effect of secondary carbides addition on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-based cermets

(Ti, W, Mo, V)(C, N)-based cermets were prepared by mixing Mo₂C, WC and TaC with ultrafine (Ti, W, Mo, V)(C, N) powders, and then processed via a conventional P/M technique. The effect of Mo₂C, WC and TaC on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co systems was investigated. The Mo₂C content was varied from 0 to 10 wt.% and additive WC or TaC was added at a level of 5 wt.% with Mo₂C addition. The results show that the densification of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co cermets was improved significantly by the addition of Mo₂C. With the increase of Mo₂C content, there is a coarsening tendency in the microstructure of (Ti, 20W, 15Mo, 0.2V)(C, N)-8Ni-7Co system, but the refinement for (Ti, 15W, 5Mo, 0.2V)(C, N)-8Ni-7Co. TaC addition decreases the density of (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-8Ni-7Co cermet and thus weakens its bending strength. (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo₂C-5WC-8Ni-7Co cermet has optimal mechanical properties: bending strength of 1999 MPa, hardness (H_v) of 1677 MPa and toughness of 9.95 MPa m^1/2 respectively by adding WC, which is due to its ultrafine and weak core/rim structure.     

化学成分对TiC-Ni系金属陶瓷显微组织的影响

为探究Mo、WC、ZrC对TiC-Ni系金属陶瓷组织的影响,真空烧结制备了TiC- Ni系金属陶瓷。利用X射线衍射仪(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscope,SEM)、能谱仪(energy dispersive spectrometer,EDS)等研究了Mo、WC和ZrC对金属陶瓷显微组织的影响。结果表明,TiC基金属陶瓷的显微组织随着Mo、WC、ZrC的加入而逐渐细化,形成(Ti,Mo)C、(Ti,Zr,Mo)C、(Ti,Mo,W)C、(Ti,Zr,Mo,W) C、(Zr,Ti,Mo)C和(Zr,Ti,Mo,W)C等固溶体,并且在10%TiC-40%ZrC-14%Mo-15% WC-20%Ni-1%C试样中出现了无芯晶粒(coreless grains)、微裂纹及微孔洞。断裂韧性测试结果表明,该显微结构能大大提高材料的断裂韧性。     

Effect of WC content on the microstructure and mechanical properties of Ti(C0.5N0.5)–WC–Mo–Ni cermets

Ti(C_0.5N_0.5)–xWC–Mo–Ni system cermets were studied to investigate the effect of WC content on the microstructure and mechanical properties. The results showed that the lattice constant of Ti(C,N) hard phase in the Ti(C_0.5N_0.5)–WC–Mo–Ni system increases with the increase of WC content, but it is smaller than that in Ti(C_0.7N_0.3)–WC–Ni system. The microstructures of the cermets exhibit three kinds of grains: one has black core-grey rim structure, the second has white core-grey rim structure and the third has black core-white rim structure. The thickness of inner rim increases with the increasing of WC content. Additionally, the particle size of black core decreases with the increase of WC content in the range of 0–10 wt.%, and then increases slightly with further increase of WC. The TRS increases with the increase of WC content, but hardness decreases with the increase of WC content.     

不同碳/氮比的Ti(C x , N1- x )基金属陶瓷的显微组织与性能

Ti(C_x,N_1-x)基金属陶瓷是用不同碳氮比制造的。研究了碳/氮比对芯-环结构和金属陶瓷性能的影响。结果表明，由于孔太多， Ti(C_0.5,N_0.5)基金属陶瓷的性能较差。随着碳/氮比的增加，白核/灰环的形成率降低，并且微观结构的均匀性增强。因此，基于 Ti(C_0.7,N_0.3)的金属陶瓷显示出优异的力学性能，但有少量的孔隙和较低的相对密度。与Ti(C_0.7,N_0.3)基金属陶瓷相比，TiC基金属陶瓷在没有N元素的情况下具有较高的相对密度且无孔隙，但其晶粒较粗大。为了获得细晶粒和高密度的显微组织，将0.25%Cr₃C₂-0.75%VC（质量分数）引入到TiC基金属陶瓷中，获得了优异的硬度、横向断裂强度和韧性。另外，在Ti(C_0.7,N_0.3)基金属陶瓷中也添加了0.25%Cr₃C₂-0.75%VC，但其力学性能低于Ti(C_0.7,N_0.3)的金属陶瓷，这是因为细颗粒和反应颗粒与Ti(C,N)发生了急性固溶反应。研究了基于不同C/N比的Ti(C_x,N_1-x)基金属陶瓷的切削性能和摩擦性能。结果表明，具有0.25%Cr₂C₃-0.75%VC的TiC基金属陶瓷在室温下的摩擦系数最低，为0.15，在1000 r/min的高速切削过程中，使用寿命最长。     

Microstructural investigation and machining performance of NbC-Ti(C0.5N0.5) matrix cermets

In this study, Ni or Co + Ni bonded NbC matrix cermets with secondary carbides (Mo₂C and WC) as well as Ti(C_0.5N_0.5) were prepared by liquid phase sintering at 1450 °C in vacuum. Detailed microstructural investigation was performed by SEM, EPMA and XRD analysis. The microstructure, mechanical properties as well as the C45 (HB140) steel turning performance of the cermets were investigated, and compared with a commercial Ti(C_0.5N_0.5) based cutting insert. The sintering results indicated that the partial substitution of NbC by Ti(C_0.5N_0.5) had a significant effect on the core-rim microstructure and refinement of NbC solution grains, as well as improved mechanical properties of the NbC-Ti(C_0.5N_0.5) cermets. The phase constitution and composition of the cermets were supported by thermodynamic equilibrium calculations. All sintered cermets were composed of a fcc solid solution metal binder and a cubic core-rim NbC based solution phase, as well as an independent N-rich Ti(C,N) phase. The NbC-Ti(C_0.5N_0.5) and Ti(C_0.5N_0.5) matrix cermets had a comparable HV₃₀ of 1500–1600 kg/mm² and a similar fracture toughness of 8.0 MPa m^1/2.     

烧结气氛对Ti(CN)基金属陶瓷组织和性能的影响

用X射线衍射、背散射扫描电镜及能谱仪等分析手段研究了烧结气氛(真空、N2、Ar)对不同成分TiC基和Ti(CN)基金属陶瓷合金显微组织和性能的影响.金属陶瓷在N2和Ar中烧结后,合金碳含量比在真空中烧结的碳含量低0.5%左右;在N2中烧结后,合金的氮含量提高了0.5%左右.环状结构心部可以是以钨等重金属元素为主要成分的碳化物,也可以是以钛为主要成分的碳化物和碳氮化物.环状结构为金属元素含量和分布不同的(Ti,W,Ta,Mo,Co,Ni)(C,N)固溶体,粘结相是与Ti,W,Ta,Mo,C,N等元素有不同溶解度的钴镍固溶体.真空烧结后组织结构比较均匀,合金的性能最好.在Ar、N2中烧结后,气氛中的氧和氮参加烧结反应,影响合金成分碳氮平衡,在合金表面形成壳层结构,产生表面缺陷,合金的密度、显微硬度、抗弯强度均有比较大的降低;N2气氛影响更大.     

Lightweight TiC/Ti wear-resistant coatings for lightweight structural applications

Lightweight coatings based on titanium and titanium carbides produced by plasma spraying can be used to improve and modify the tribomechanical properties of aerospace structural materials. Although plasma-sprayed WC/Co coatings have been applied with success in many cases, such as primary wear-re-sistant materials, their high densities preclude their use in applications that mandate reduction in weight. In the present investigation, the sliding wear resistance of plasma-sprayed, metal-bonded TiC coatings on AI 7075 substrates was studied. Coatings containing 50, 70, and 90 vol% TiC in a Ti matrix produced from physically blended powders of Ti and TiC were compared. Metallographie evaluations showed that dense coatings with good bonding to AI 7075 substrates can be obtained. Coatings from commercial pu-rity (CP) Ti powders sprayed in air under atmospheric conditions, however, indicated considerable oxi-dation of the particles. Under dry sliding conditions, the coefficient of friction (COF) values of the Ti/TiC containing/Al 7075 substrate system were lower than high-velocity oxygen fuel (HVOF) sprayed 75% Cr₃C₂/25%NiCr coatings on steel and were comparable to coatings of WC/Co. Vacuum plasma-sprayed TiC/Ti coatings with 90 vol% TiC also exhibited better wear resistance than HVOF sprayed 75%Cr₃C₂/25%NiCr.     

Microstructure and mechanical properties of (Ti,W,Ta)C-xMo-Ni cermets

(Ti,W,Ta)C-xMo-20Ni (x = 0–20 wt.%) system cermets were prepared by using (Ti,W,Ta)C solid solution as hard phase, without adding secondary carbides in this work. The microstructures exhibited two kinds of carbide grains observable in the BSE mode: one had a dark core–gray rim structure; the other had a dark core–white inner rim–gray outer rim structure. Several (Ti,W)C white particles with high W content were also observed in the microstructures. Results showed that molybdenum has completely dissolved in the Ni binder and mainly was found in the rims of the carbide particles. As the Mo content increased, the wettability between (Ti,W,Ta)C particles and metallic phase was improved, and the shrinkage of cermets increased, the porosity decreased. Results also revealed that finer microstructures were obtained with the increase of Mo addition. But excess Mo addition caused the aggregation of particles. Mechanical properties such as hardness and TRS improved with the increase of Mo content, but the TRS of cermets reached a peak value at the 15 wt.% Mo addition, then declined with the further increase of Mo addition.     

Effect of the Cr content on the sintering behaviour of TiCN–WC–Ni–Cr3C2 powder mixtures

In TiCN–W–Cr–Ni cermets produced by liquid phase sintering melting occurs at lower temperatures as their Cr content increases. For low Cr additions (up to 4 wt.%) eutectic temperatures are close to those found in the TiC–WC–Ni system. For 8 wt.% Cr and above, temperatures are similar to those found in the Cr–Ni–C system. The precipitation of M₇C₃ carbides is observed to start at 8 wt.% Cr in samples sintered at 1425 °C for 1 h. This sets a limit for the Cr solubility in the binder phase of these cermets around 18 wt.%. The dissolution of WC and Cr₃C₂ particles starts at temperatures as low as 1150 °C, but that the homogenization of the binder phase is only achieved after melting. The carbonitride phase exhibits the typical precipitation of inner and outer rims onto Ti(C,N) cores. However, a fine precipitation of Ni-rich particles is found inside Ti(C,N) cores, likely related to coalescence phenomena.     

Fundamentals of liquid phase sintering for modern cermets and functionally graded cemented carbonitrides (FGCC)

Metallurgical reactions and microstructure developments during sintering of modern cermets and functionally graded cemented carbonitrides (FGCC) were investigated by modern analytical methods such as mass spectrometer (MS), differential thermal analysis (DTA), differential scanning calorimeter (DSC), dilatometer (DIL), microscopy and analytical electronic microscopy with energy dispersive spectrometer (EDS). The complex phase reactions and phase equilibria in the multi-component system Ti/Mo/W/Ta/Nb/C,N-Co/Ni were studied. The melting behavior models in the systems of TiC–WC/MoC–Ni/Co, TiC–TiN–WC–Co and TiCN–TaC–WC–Co have been established. By an in-depth understanding of the mechanisms that govern the sintering processing and metallurgical reactions, new cermets and different types of FGCC with desired microstructures and properties were developed.     

On the use of TiO2 in Ti(C,N)-WC/Mo2C-(Ta,Nb)C-Co/Ni cermets

In this study, Ti(C,N)-WC/Mo₂C-(Ta,Nb)C-Co/Ni cermets with varying [Mo]/([W] + [Mo]) mole ratios and constant [W] + [Mo] content were prepared by using TiO₂ and carbon as substitutes for a part of Ti(C,N). In situ carbothermal reaction took place with subsequent liquid phase sintering. The thermal behavior and outgassing behavior were conducted using differential thermal analysis/thermal gravity analysis (DTA-TG) and mass-spectrometric evolving gas analysis (MS-EGA). The microstructure was investigated by scanning electron microscopy (SEM). After being sintered in N₂ atmosphere, cermets without TiO₂ additions generally showed rimless microstructures with black grains independently distributed from other phases, whereas the cermets with TiO₂ addition showed complete core-rim microstructures. The average grain size generally decreased with increasing Mo content, and increased with increasing TiO₂ substitution. Moreover, the average grain size increased with decreased N₂ pressure from 50 mbar to 10 mbar at any [Mo]/([Mo] + [W]) ratio. The most interesting result was for the Mo-free cermets with 5 mol% TiO₂ and 10 mol% TiO₂ addition sintered in 50 mbar N₂: both the hardness and fracture toughness increased compared with the cermets without TiO₂ addition. The HV-K_IC behavior of the majority of the cermets was superior to the industrial grades.     

Erosion-corrosion behavior of Ti(C,N)-based cermets containing different secondary carbides

The present work investigated the effects of secondary carbides (Mo₂C\WC\TaC\NbC) on the erosion-corrosion behavior of Ti(C,N)-based cermets. The results indicate that the erosion-corrosion resistance of Ti(C,N)-based cermets is enhanced in the order of NbC, TaC, WC and Mo2C addition. The contribution of erosion to the erosion-corrosion of Ti(C,N)-based cermets is much more significant than that of corrosion, and it increases with the decreased mechanical properties. The synergistic effect plays a dominant role in the degradation of Ti(C,N)-based cermets in erosion-corrosion conditions. There are two modes to ceramic phase degradation in erosion conditions: large ceramic grains are prone to deterioration through crack initiation and propagation → grain fracture → fragment removal; finer ceramic grains trend to be pulled out after the deterioration of binder and interface. The binder loss is determined by the corrosion resistance of binder, the erosion resistance of binder and the erosion resistance of ceramic phase.     

Mo含量对TiC基金属陶瓷 组织和力学性能的影响

采用粉末冶金工艺制备了6组不同Ni、Mo添加量的金属陶瓷材料.通过扫描电镜观察组织结构、断口形貌及裂纹扩展,用三点弯曲法测试抗弯强度,用洛氏硬度计测得试样硬度.试验结果表明,添加Mo后,TiC基金属陶瓷呈现出典型的芯壳结构,组织细化明显.当TiC含量为70%、Ni∶Mo=2 ∶ 1时,材料的抗弯强度、硬度与断裂韧性综合...     

The reciprocating wear behaviour of TiC–Ni3Al cermets

TiC-based cermets have become more popular as a replacement to traditional WC–Co ‘hardmetals’ due to their superior mechanical properties at elevated temperatures, improved corrosion resistance and significantly lower density. The current study assesses the reciprocating wear response of TiC–Ni₃Al cermets fabricated by melt infiltration, with Ni₃Al binder contents ranging from 20 to 40 vol.%. Wear testing was performed using a ball-on-flat geometry, with a WC–Co sphere used as the counter-face material. It is demonstrated that the cermets are affected by similar wear mechanisms for each of the binder contents, but displayed the lowest wear when prepared with 30 vol.% Ni₃Al. Additionally, the 40 vol.% samples displayed a clear transitional behaviour, with an improved wear resistance comparable to the 30 vol.% samples at low applied loads, but a degraded wear response comparable to the 20 vol.% samples at high applied loads.     

Effect of partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)-Ni-based cermets

Four cermets of composition TiC-10TiN-16Mo-6.5WC-0.8C-0.6Cr₃C₂-(32 − x)Ni-xCr (x = 0, 3.2, 6.4 and 9.6 wt%) were prepared, to investigate the effect of the partial substitution of Cr for Ni on densification behavior, microstructure evolution and mechanical properties of Ti(C,N)-Ni-based cermets. The partial substitution of Cr for Ni decreased full densification temperature, and the higher the content of Cr additive was, the lower full densification temperature was. The partial substitution of Cr for Ni had no significant effect of the formation of Mo₂C and Ti(C,N) and the dissolution of WC, and however, it had a significant effect on the dissolution of Mo₂C. Cr in Ni-based binder phase diffused into undissolved Mo₂C to form (Mo,Cr)₂C above 1000 °C at 6.4-9.6 wt% Cr additive, and a small amount of (Mo,Cr)₂C did not dissolve after sintering at 1410 °C for 1 h at 9.6 wt% Cr additive. In the final microstructure, Cr content in Ni-based binder phase increased with increasing the content of Cr additive, and however, regardless of the content of Cr additive, coarse Ti(C,N) grains generally consisted of black core, white inner rim and grey outer rim, and fine Ti(C,N) grains generally consisted of white core and grey rim. The partial substitution of Cr for Ni increased hardness and decreased transverse rupture strength (TRS). Ni-based binder phase became hard with increasing the content of Cr additive, therefore resulting in the increase of hardness and the decrease of TRS. TRS was fairly low at 9.6 wt% Cr additive, which was mainly attributed hardening of Ni-based binder phase and undissolved (Mo,Cr)₂C.     

Influence of WC addition on the microstructure and mechanical properties of NbC–Co cermets

NbC–24.5 wt.% Co cermets with up to 30 wt.% WC were obtained by solid state hot pressing at 1300 °C under a pressure of 45 MPa for 10 min and pressureless liquid phase sintering at 1360 °C for 60 min. The effect of WC addition on the microstructure and mechanical properties of NbC–Co based cermets was investigated. The hot pressed cermets exhibited interconnected and irregular niobium carbide (NbC) or (Nb,W)C grains, whereas the shape of the NbC grains changed from faceted with rounded corners to spherical, as the WC content increased in the pressureless sintered cermets. The undissolved WC increased with increasing WC addition. A clear core/rim structure was observed in the hot pressed cermets with 10–30 wt.% WC additions, whereas this structure was gradually eliminated when pressureless sintering. The hardness remains nearly constant whereas the fracture toughness slightly increases with increasing WC addition. The dissolution of WC in the Co binder and NbC grains, as well as the formation of a solid solution (Nb,W)C phase were supported by thermodynamic calculations.     

Effect of Mo addition on microstructure and mechanical properties of (Ti,W)C solid solution based cermets

(Ti,W)C solid solution was synthesized by milling a mixture of C and oxides and then reducing it at 1350 °C for 2 h. The microstructure and mechanical properties of (Ti,W)C solid solution based cermets with various Mo additions were systemically studied. The dark core–gray rim carbide grains and/or gray carbide grains embedded in black Ni based binder phase were observed. The grain size of the cermets decreased with increasing Mo addition, while excessive Mo addition would result in agglomeration and inhomogeneity of the grains. The dark core was transformed from (Ti,W)C into (Ti,W,Mo)C and Mo concentration in the dark core increased with increasing Mo content. The fracture toughness of the cermets decreased with the increase of Mo content, while the hardness and TRS reached a peak value at 10 wt.% and 15 wt.% Mo additions respectively, and declined with the further increase of Mo content.     

Effects of Ti addition on microstructure homogenization and wear resistance of wide-band laser clad Ni60/WC composite coatings

Ni60/WC composite coatings were fabricated by wide-band laser cladding. The effects of Ti addition on microstructure homogenization and coating properties were investigated. Coating microstructure, phase constitution, microhardness and wear resistance were studied and grading analysis of in-situ synthesized ceramic particles was carried out. Results indicated that ceramics particles of Cr₅B₃ and M₂₃C₆ (M represents for Cr and W) carbides were in-situ synthesized in original Ni60-20WC coatings. With Ti addition, dissolution of original WC was facilitated and lots of TiC particles were synthesized instead of M₂₃C₆ carbides. Furthermore, the block Cr₅B₃ particles were greatly homogenized due to the net structure formed by dispersive TiC particles. With Ti addition, D50 of particle size decreased from 8.94 μm to 4.45 μm and particle morphologies were transformed from star-like shapes to uniform square blocks. Microhardness distribution became more uniform with average value decreased from 799 ± 89 HV_0.2 to 744 ± 77 HV_0.2. Due to the homogenized ceramic particles, wear resistance of coatings with Ti addition was enhanced to 2.6 times that of the original coatings.