Shuai Ma,Di Dong,Mengyao Zhang,Ye Gao,Zhuangzhi Wu,Dezhi Wang
W-Re-HfC alloys have been extensively applied in the field of high-temperature structural parts. To ensure high temperature reliability, it is essential to enhance creep resistance ability. In this study, the microstructures of forged W-Re-HfC alloys were adjusted using different heat treatment processes . The corresponding tensile creep properties were also measured at 2000 °C with 40 MPa. Furthermore, a possible creep fracture mechanism was also explored. The forged W-Re-HfC sample annealed for 2 h exhibited the best creep performances with a steady-state creep rate of 3.28 × 10 −6 and a creep life of 5.6 h. Generally, a larger grain size indicates a lower steady-state creep rate; however, the precipitation of carbides at the grain boundaries (GBs) deteriorates the bonding strength of interfaces, thus reversing the former trend. The dominant creep mechanism is diffusion creep , in which the voids nucleate perpendicular to the GBs, grow and connect into cracks, ultimately leading to fractures.
Faqiang Shi,Limeng Liu,Zhaoping Hou,Guihong Geng,Yujin Wang
Tantalum carbide ceramics with an overall composition of TaC 0.6 were prepared by hot pressing at 1700 °C for 1 h under 30 MPa pressure with fcc TaC and bcc Ta powder as starting materials. Effects of adding 0–30 mol% Cu on densification, phase formation, microstructural evolution , mechanical properties and electrical conductivity of the obtained composite ceramics were investigated. Full density could be reached at 20 mol% Cu addition and above. Reactions between TaC and Ta resulted in the final phases of hexagonal Ta 2 C and rhombohedral ζ-Ta 4 C 3-x . Plate-shaped ζ laminate grew in both TaC and Ta 2 C and consequently had their sizes confined by the parental grains. Addition of 20–30 mol% Cu could significantly grow the intermediate Ta 2 C grains, hence controlling length of the ζ laminates precipitated in them to form bimodal microstructures consisting of large grains. The 20 mol% Cu composition had a better flexural strength (706 ± 46 MPa) and fracture toughness (9.2 ± 1.7 MPa m 1/2 ). Electrical resistivity at room temperature of the composites decreased with Cu content from 1.03 μΩ m at 0 mol% addition to 0.12 μΩ m at 30 mol% Cu.
Al 2 O 3 –ZrO 2 (3Y)–SiC ceramic composites were prepared by spark plasma sintering in vacuum under 40 MPa of uniaxial compression between 1300 °C and 1400 °C. The effect of nano-size SiC and sintering temperature on the microstructure and mechanical properties of ceramic composites were investigated. The results showed that SiC particles was uniformly distributed in the composite, mainly within the matrix grains. Sintering temperature and SiC particles caused the shape of alumina grains to be columnar. The flexural strength of 22.3 vol% Al 2 O 3 -57.7 vol% ZrO 2 -20 vol% SiC sintered at 1350 °C composites was 1081 MPa, fracture toughness was 15.18 MPa m 1/2 and hardness was 16.42 GPa. The addition of SiC particles leads to grain boundary strengthening, and the change of fracture mode and cracks deflection and bridging are considered to be the main reasons for the increase in material fracture toughness.
Xinjiang Zhang,Feng Song,Zhiping Wei,Wenchao Yang,Zhongkui Dai
In-situ TiC/Ti titanium matrix composites were successfully fabricated through a novel approach, utilizing the reaction of graphene and Ti mixture powders in spark plasma sintering . Microstructure, hardness and compressive properties of such composites were investigated. The layered graphene nanosheets as the carbon source were dispersed in the powders, and subsequently formed uniform TiC particles in Ti matrix during the rapid sintering. The resulting TiC particles exhibited the micro- and nano-sized equiaxial structures. Such composites possessed the significantly enhanced hardness and room-temperature compressive strength comparing with the as-cast and as-sintered pure Ti. The ultimate and yield compressive strengths of as-prepared 7.0 vol% TiC incorporated composite respectively reached up to 2.64 GPa and 1.93 GPa, beyond some advanced Ti materials reported to date. In-situ micro- and nano-sized TiC particles were believed to be beneficial to harden and strengthen Ti matrix. The relevant strengthening mechanisms of such composites were discussed.
危险品化学品经营许可证（带存储）