Spark plasma sintering of quadruplet ZrB2–SiC–ZrC–Cf composites

Spark plasma sintering (SPS) route was employed for preparation of quadruplet ZrB₂–SiC–ZrC–C_f ultrahigh temperature ceramic matrix composites (UHTCMC). Zirconium diboride and silicon carbide powders with a constant ZrB₂:SiC volume ratio of 4:1 were selected as the baseline. Mixtures of ZrB₂–SiC were co-reinforced with zirconium carbide (ZrC: 0–10 vol%) and carbon fiber (C_f: 0–5 vol%), taking into account a constant ratio of 2:1 for ZrC:C_f components. The sintered composite samples, processed at 1800 °C for 5 min and 30 MPa punch press under vacuumed atmosphere, were characterized by densitometry, field emission scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry as well as mechanical tests such as hardness and flexural strength measurements. The results verified that the composite co-reinforced with 5 vol% ZrC and 2.5 vol% C_f had the optimal characteristics, i.e., it reached a relative density of 99.6%, a hardness of 18 GPa and a flexural strength of 565 MPa.     

Preparation and characterization of three-dimensional carbon fiber reinforced zirconium carbide composite by precursor infiltration and pyrolysis process

Three-dimensional carbon fiber reinforced zirconium carbide composite (3D C/ZrC) was fabricated for ultra high temperature applications by precursor infiltration and pyrolysis (PIP) process using the mixture of zirconium butoxide (Zr(OC₄H₉)₄) and divinylbenzene (DVB) as precursor of zirconium carbide. The micro-structural, mechanical and ablative properties of the 3D C/ZrC composite were studied. The flexural strength of the composite was 107.6 MPa, the elastic modulus was 28.8 GPa, and the fracture toughness was 7.03 MPa m^1/2. The mass lose rate and linear recession rate of the 3D C/ZrC composite during oxyacetylene torch test was 0.012 g/s and -0.002 mm/s, respectively. The formation of ZrO₂ melt on the surface of the composite contributed mainly the excellent ablative property.     

液相先驱体转化结合溶胶凝胶法合成ZrC-SiC纳米复合粉体

以八水合氧氯化锆为锆源、正硅酸乙酯为硅源、蔗糖为碳源,采用液相先驱体转化结合溶胶凝胶法合成ZrC-SiC纳米复合粉体.借助傅立叶红外光谱仪分析了有机锆先驱体的官能团,借助X射线衍射仪和扫描电子显微镜研究了Si/Zr摩尔比对复合粉体物相组成与显微形貌的影响.研究表明:有机锆先驱体具有链状或网状结构;1450℃烧成并保温2 h,Si/Zr摩尔比0.28时复合粉体中仍存在未反应的m-ZrO2相,Si/Zr摩尔比增加至1.11、2.56、5.88、23.17时均合成了纯相ZrC-SiC纳米复合粉体;随着Si/Zr摩尔比的增加,复合粉体粒径变化不大;Si/Zr摩尔比为2.56时平均粒径仅90 nm,且元素分布均匀.     

Plasma arc welding of ZrB2–20 vol% ZrC ceramics

Zirconium diboride ceramics containing 20 vol% zirconium carbide were preheated to 1450 °C and plasma arc welded to produce continuous joints. Arc welding was completed using a current of 198 A, plasma flow rate of 0.75 l/min, and welding speed of ∼8 cm/min. Two fusion zones, having penetration depths of 4.4 and 2.3 mm, resulted in different microstructures. One fusion zone contained ZrB₂ crystals, up to ∼1 mm in length, and a ZrB₂–ZrC eutectic. The second fusion zone revealed ZrB₂ and ZrC, along with C that was attributed to diffusion from the graphite support used during welding. ZrB₂ and ZrC grains in the latter fusion zone were asymmetric, having an average maximum Feret diameter of 52.4 ± 53.2 μm and 10.8 ± 8.1 μm, respectively. Hardness, used to identify a heat affected zone for both weldments, increased from 12 GPa at the fusion zone boundary, to the hardness of the parent material, 15.2 ± 0.1 GPa.     

Ablation behavior of a network interlacing ZrC-VC ceramic coating prepared by a pioneering spillover permeation

A novel network interlacing ZrC-VC ceramic coating was prepared by a pioneering spillover permeation. With the increase of Zr content in the blind vias, the content of ZrC in the coating and the density of the coating all decrease. The density of the coating on C/C–ZrC–SiC substrate is obviously higher than that on C/C substrate. The linear ablation rate of the novel ceramic coated C/C–ZrC–SiC composites was ?0.06 μm/s with about 20 and 1.56 times reduction than C/C composites and C/C–ZrC–SiC composites respectively. The improved ablation resistance was attributed to a dense honeycomb ZrO₂ layer filled with liquid vanadium oxide in the ablation center and the improved thermal radiation.     

添加ZrC对TiC基金属陶瓷力学性能的影响

采用粉末冶金方法真空烧结制备了添加Zrc的TiC基金属陶瓷,研究了ZrC的不同添加量对TiC基金属陶瓷力学性能的影响.结果表明:ZrC溶解形成了(Zr,Ti)C固溶体;材料典型的断裂方式为沿晶断裂和穿晶断裂;ZrC含量在30 wt%时其断裂韧性最高,而由于Ni对ZrC润湿性不理想导致抗弯强度和硬度都有不同程度的降低.     

Near-net shape manufacture of B4C–Co and ZrC–Co composites by slip casting and pressureless sintering

Fabrication of near-net shaped B₄C–Co and ZrC–Co composites by slip casting and pressureless sintering is described. It is shown how B₄C–Co and ZrC–Co concentrated suspensions can be prepared by aqueous colloidal processing, and optimized (in terms of pH, deflocculant contents, and sonication time) to have a shear-thinning rheological behaviour suitable for the near-net shaping of the corresponding cermet compacts by slip casting. It is also demonstrated that the robust, highly-dense compacts so obtained have a uniform green microstructure without macro-defects or gradient density, and which can be fully densified by pressureless sintering. Specifically, it is shown that B₄C–Co compacts densify by reactive and transient liquid-phase sintering, thus resulting in multi-component ceramics. ZrC–Co compacts densify however by persistent liquid-phase sintering, thus resulting in cermets. An explanation is given for these observations, and general implications are discussed for the near-net shape manufacture of these and similar carbide-metal composites for use in engineering applications.     

Effect of MoSi2 content on the lubricated sliding-wear resistance of ZrC-MoSi2 composites

The effect of MoSi₂ content (5, 10, and 20 vol.%) on the lubricated, sliding-wear behaviour of ZrC-MoSi₂ composites at room temperature is investigated and modeled. It was found that the resistance to sliding wear decreases markedly with increasing MoSi₂ content, with a greater rate of mild wear, an earlier transition from mild to severe wear, but essentially the same rate of severe wear. The analysis of the wear results using a mechanistic model indicated that the worsened sliding-wear resistance with the increase in MoSi₂ content derives from the decreased hardness and increased internal effective tensile stresses of the ZrC-MoSi₂ composite, which speed up the accumulation of damage induced by plastic deformation within the grains and shorten the onset of the grain-boundary fracture condition and subsequent grain pullout. Reduction of the MoSi₂ content thus emerges as an effective approach for making the ZrC-MoSi₂ composites more sliding-wear resistant under lubrication at room-temperature. These results may have important implications because ZrC holds promise for use in tribological applications requiring both wear resistance and electrical contact, and MoSi₂ is its commonest sintering additive.     

添加微米级ZrC颗粒的低碳微合金钢力学性能研究

真空条件下,在低碳微合金钢中添加体积分数为1.1%的微米级ZrC陶瓷颗粒,在φ450 mm热轧试验机上进行轧制,轧后钢板晶粒被细化到5.5μm,其抗拉强度和屈服强度分别达到635 MPa和517.5 MPa,维氏硬度(HV5)达到214.zrC颗粒对试验钢具有明显的强化作用,在试验钢凝固结晶和后期轧制过程中均起到细化晶粒的作用.热轧钢板的显微组织为铁素体,钢中夹杂物弥散分布.     

Relationship analyses on environmental factors-ablation performance based on ZrC-TaC system: Oxygen partial pressure and gas flow scouring

For better understanding on effects of ablation environmental factors (oxygen partial pressure P(O₂) and gas flow scouring), multiple experiments and multiscale simulations based on thermally sprayed ZrC-TaC system were conducted. High P(O₂) was found helpful to accelerate Ta₂O₅/ZrO₂ mutual diffusion by variable P(O₂) oxidation at 1500 ℃ (5–50 kPa). Effects of gas flow scouring was evaluated by flow filed simulation coupling laser and oxyacetylene ablations, from which its promotion effect on Ta₂O₅/ZrO₂ diffusion efficiency was found. The increased Ta₂O₅/ZrO₂ diffusion efficiency will accelerate the structure instability of Ta doped c-ZrO₂ skeletons due to Zr-O bond length extension around Ta atoms.