Mo_2C对Ti(C,N)基金属陶瓷腐蚀性能的影响

通过静态浸泡腐蚀和动电位极化两种方法,研究了Mo2C对Ti(C,N)基金属陶瓷在NaOH溶液中腐蚀性能的影响。实验结果表明:Ti(C,N)基金属陶瓷的耐蚀性明显优于WC-Co硬质合金;添加Mo2C可以大幅度提高Ti(C,N)基金属陶瓷的机械性能,硬度从91.2到94.0 HRA和抗弯强度从930到1 350 MPa,但会降低金属陶瓷的耐蚀性能;由于Mo2C的加入,会使金属陶瓷的动电位极化曲线出现两个钝化区,但是两个钝化区域的电流均未达到真正的钝化电流(10-5A/cm2),因而这些钝化现象均为伪钝化;在经动电位极化后的试样表面,粘结相Ni和白色的内环相均会被腐蚀,其中内环相为富Mo的(Mo,Ti)(C,N)固溶体,其耐腐蚀性较未溶的Ti(C,N)芯更差。随着Mo2C添加量的提高,内环形相的厚度随之会增加,从而降低了Ti(C,N)基金属陶瓷的耐蚀性能。     

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.     

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.     

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 WC addition and cooling rate on microstructure,magnetic and mechanical properties of Ti(C0.6,N0.4)-WC-Mo-Ni cermets

Ti(C_0.6,N_0.4)-8Mo-xWC-25Ni (x = 0, 3, 6 and 9 wt%) cermets were synthesized under different cooling rates by vacuum sintering. The influence of WC addition and cooling rate on microstructure, magnetic and mechanical properties of the as-prepared Ti(C,N)-based cermets was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The results revealed that the grain size of the Ti(C,N)-based cermets became finer with WC addition. Furthermore, room-temperature saturation magnetization (M_s), remanence (M_r) and Curie temperature (T_c) of the Ti(C,N)-based cermets initially decreased with increasing WC content, followed by a gradual increase. Cermets bacame paramagnetic at x = 6 under the cooling rate of 2 °C/min, x = 6 and 9 under the cooling rate 35 °C/min, respectively. The decrease in magnetic properties could be ascribed to the enhanced solid solubility of alloy elements in Ni-based binder phase. Moreover, the hardness and transverse rupture strength (TRS) of the Ti(C,N)-based cermets initially increased and followed by a gradual decrease, whereas the fracture toughness initially decreased followed by an increase with increasing WC content. At the same value of x, the Ti(C,N)-based cermets exhibited better magnetic and mechanical properties at the cooling rate of 35 °C/min than that at the cooling rate of 2 °C/min, which could be attributed to the grain refinement strengthening and solid-solution strengthening of the binder phase.     

Early high-temperature oxidation behavior of Ti(C,N)-based cermets with multi-component AlCoCrFeNi high-entropy alloy binder

The early high-temperature oxidation behavior of Ti(C,N)-based cermets with equiatomic AlCoCrFeNi high-entropy alloy binder has been studied, as well as the cermet with Ni/Co binder as a reference. Experiments were performed at the temperature range of 800–1100 °C in static laboratory air. The micro-structural evolution of the multi-layered oxide scales on the cermets was investigated and the effect of binder phase constituent on the oxidation characteristics of Ti(C,N)-based cermets was evaluated. The results demonstrated that the cermet with AlCoCrFeNi multi-element alloy binder possesses superior oxidation resistance, which is greatly better than that of the cermet with Ni/Co metallic binder under the same condition. We suggest that the formation of a continuous and dense external oxide scale can effectively impede the outward diffusion of volatile tungsten oxides and inward oxygen transport, leading to a remarkable improvement of oxidation resistance. In addition, the enhanced oxidation resistance was related to the high Cr and Al concentration in AlCoCrFeNi binder phase that urges the formation of oxide layers with more efficient passivation effect against oxidation.     

The influence of Ni3Al binder content on the aqueous corrosion response of TiC and Ti(C,N) cermets

In the current work the corrosion mechanisms of Ti(C,N) based cermets are analysed in a 3.5 wt.% NaCl aqueous solution. The effects of varying the Ni₃Al intermetallic binder content are assessed, with either 20 or 30 vol.% binder used. The assessment of corrosion involved a variety of electrochemical measurements, including open circuit potential, along with anodic and cathodic potentiodynamic polarisation. Both the corrosion potential and current density were determined from Tafel extrapolation, which allowed an estimation of the cermet corrosion rates. It is demonstrated that the primary corrosion mechanism for these cermets involves dissolution of the intermetallic phase during oxidation attack, and thus this response increases with the amount of binder in the cermet. It was also observed that addition of N to the Ti(C,N) ceramic phase is beneficial to the corrosion characteristic the cermets, due to significant refinement of the grain size of the hard phase.     

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.     

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.     

The effects of C:N ratio on the aqueous corrosion response of TiC and Ti(C,N) cermets with a Ni3Al-based binder

The aqueous corrosion behaviour of TiC and Ti(C,N) based cermets, sintered with 30 vol.% Ni₃Al binder, has been investigated. For comparison purposes, the single-phase constituents were prepared using spark plasma sintering (SPS). The potentiodynamic and cyclic polarisation responses of the cermets and single-phase materials have been determined. Post-test corrosion solutions were analysed using inductively coupled plasma optical emission spectrometry, while samples were evaluated using scanning electron microscopy and associated energy dispersive X-ray analysis. Selective attack of the binder occurs, while the extent of corrosion and primary operative mechanism depends on the C:N ratio in the Ti(C,N).     

Microstructure and fracture toughness of Ti(C0.7N0.3)-WC-Ni cermets

Mo₂C is normally added to improve the wettability between Ti(C,N) and Ni in Ti(C,N)-based cermets. Due to the increasing price of Mo₂C, much attention has been paid to Ti(C,N)-based cermets with WC addition. In this paper, effect of WC content on the microstructure and properties of Ti(C_0.7N_0.3)-xWC-15wt.%Ni cermets free of Mo₂C was studied. The experimental results show that the microstructure is refined obviously with the increase of WC content. The fracture toughness decreases with the increase of WC content when WC content is 10-25 wt.%, and increases when WC content varies from 25 wt.% to 30 wt.%.     

Thermodynamics of TiC- and Ti(C,N)-based cermet processing prior to liquid phase sintering stage

The thermodynamics of the various events occurring during heating to liquid phase sintering temperatures of powder compacts of TiC- and Ti(C,N)-based cermets has been investigated. The results show that via a series of dissolution, solute repartitioning and mixed rim formation reactions, Mo₂C can not only help keep the systems free of oxides and residual oxygen but also moderate the Ti content in the Ni binder phase during the heating stage, thus prevent the formation of intermetallic compound and ensure good wetting in the subsequent liquid phase sintering stage.     

纳米TiN改性Ti(C,N)基金属陶瓷的抗热震性能

为研究不同粘结相对纳米TiN改性Ti(C,N)基金属陶瓷抗热震性能的影响,真空烧结制备了粘结相质量分数分别为20%Ni、10%Co-10%Ni和20%Co的Ti(C,N)基金属陶瓷。采用扫描电镜研究了材料的组织,并测量了力学性能。采用压痕-急冷法主要研究了其抗热震性能,结果表明,随着温度的升高和热循环次数的增加,裂纹增长,粘结相为Ni的金属陶瓷的抗热震性优于粘结相为Co的金属陶瓷。显微照片表明,裂纹主要沿硬质相/粘结相界面及粘结相扩展。     

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...     

Ti(C,N)基金属陶瓷的耐腐蚀性

研究了Ti（C,N）基金属陶瓷在5％HNO3、50％NaOH溶液中的耐腐蚀性能,对比了金属陶瓷与YG8硬质合金在同种腐蚀介质中的耐蚀性优劣,并对金属陶瓷在5％HNO3溶液中的腐蚀形貌进行观察。试验结果表明：金属陶瓷有良好的耐酸碱腐蚀性能,其耐蚀性与粘结相的含量密切相关,粘结相的含量愈低,耐蚀性愈好;金属陶瓷的耐蚀性明显优于YG8硬质合金;金属陶瓷的腐蚀机理为钝化膜保护的电化学腐蚀。     

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。     

Effect of grain size on corrosion behavior of electrodeposited bulk nanocrystalline Ni

Nanocrystalline (NC) and coarse-grained Ni with different grain sizes (from 16 nm to 2 μm) were fabricated by direct current electrodeposition. Effect of grain size on the electrochemical corrosion behavior of these Ni deposits in different corrosion media was characterized by using potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and immersion corrosion test. Results show that in the NaOH or NaCl solution, the NC Ni exhibits improved corrosion resistance with the decrease of grain size. But in H2SO4 solution, the higher grain boundary density accelerates corrosion due to no passive process and the corrosion resistance of NC Ni decreases with refining grain size. The distinct experimental results of NC Ni in corrosion behavior can be reasonably explained by the positive or negative effect of high-density grain boundaries in different corrosion media.     

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

Ti(C,N)-based cermets were prepared by vacuum liquid sintering. The effects of carbon content as well as cooling mode on the microstructure, magnetic and mechanical properties of the cermets were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). Hardness and transverse rupture strength (TRS) were also measured. The grains of Ti(C,N)-based cermets became finer and solid solubility of titanium, molybdenum, tungsten in binder phases decreased with increasing carbon content. The thickness of the rim phases increased when the cermet was annealed at 1360 °C for 30 min during cooling, which resulted in the decrease of the hardness and the transverse rupture strength (TRS). On the other hand, the magnetic saturation of Ti(C,N)-based cermets increased with increasing carbon content, which was due to the decrease of the solid solution of alloy elements in binder phases.     

Comparative corrosion resistance of plasma-based low-energy nitrogen ion implanted austenitic stainless steel

A high nitrogen face-centered-cubic phase (γ_N) was obtained on the nitrided surface of 1Cr18Ni9Ti austenitic stainless steel by plasma-based low-energy nitrogen ion implantation. No pitting corrosion for the γ_N phase was confirmed by electrochemical polarization measurement in 3% NaCl solution. The protective passive film with a duplex character, iron hydroxide/oxides in the outer region and chromium hydroxide/oxides and iron oxides accompanying chromium and iron nitrides in the inner region, was by 2-3 times thicker than that of original stainless steel. The thick iron hydroxide/oxides region formed on the chromium hydroxide/oxides region due to the increase of alkalinity in the solution, leading to barrier against penetration of localized attack of the aggressive ions. The equivalent general corrosion resistance for the γ_N phase was observed in 0.5 mol/l H₂SO₄ solution relative to the original stainless steel. The passive film formed on the γ_N phase in 0.5 mol/l H₂SO₄ solution was similar to that of original stainless steel. The different role of nitrogen was proposed in pitting corrosion resistance and general corrosion resistance of austenitic stainless steel.     

Ti(C,N)基金属陶瓷抗弯强度的研究

研究了提高Ti(C,N)基金属陶瓷抗弯强度的方法。采用改变粘结相成分、进行低压烧结及快冷处理来制备Ti(C,N)基金属陶瓷。试验发现,粘结相成分对材料的强度有很大的影响,提高Ni/Ni+Co的比例可以提高材料的强度,当然,在实际应用中还要考虑对其它性能的综合影响;低压烧结和快冷处理都可以有效的提高Ti(C,N)基金属陶陶的抗弯强度。