Xiangmeng Cheng

An ultra-high temperature testing instrument under oxidation environment up to 1800 °C

A new testing instrument was developed to measure the high-temperature constitutive relation and strength of materials under an oxidative environment up to 1800 °C. A high temperature electric resistance furnace was designed to provide a uniform temperature environment for the mechanical testing, and the temperature could vary from room temperature (RT) to 1800 °C. A set of semi-connected grips was designed to reduce the stress. The deformation of the specimen gauge section was measured by a high temperature extensometer. The measured results were acceptable compared with the results from the strain gauge method. Meanwhile, tensile testing of alumina was carried out at RT and 800 °C, and the specimens showed brittle fracture as expected. The obtained Youngs modulus was in agreement with the reported value. In addition, tensile experiment of ZrB2-20%SiC ceramic was conducted at 1700 °C and the high-temperature tensile stress-strain curve was first obtained. Large plastic deformation up to 0.46% and the necking phenomenon were observed before the fracture of specimen. This instrument will provide a powerful research tool to study the high temperature mechanical property of materials under oxidation and is benefit for the engineering application of materials in aerospace field.

Characterisation of graphene nanoplatelets reinforced hot pressed Ti3SiC2 ceramic

Ti3SiC2 based ceramic reinforced by 5 wt-% graphene nanoplatelets (GNPs) was prepared by hot pressing at 1550°C for 1 h under a uniaxial pressure load of 30 MPa. The effects of GNPs on the strengthening and toughening of the hot pressed Ti3SiC2 based ceramic were investigated. Comparing with t monolithic Ti3SiC2 ceramic, the flexural strength and facture toughness of the Ti3SiC2–GNP ceramic were significantly improved. The flexural strength and fracture toughness increased from 451.9 to 800.6 MPa, and from 6.23 to 9.67 MPa m1/2 respectively. The mechanism for these mechanical property improvements was attributed to the layered fracture of Ti3SiC2 grains, refined crystalline strengthening and GNP strengthening.

Surface preoxidation to improve dispersibility of zirconium diboride in aqueous medium

Abstract The dispersibility of ZrB2 particles in aqueous medium had a significant effect on colloidal forming processes of ZrB2 based ultra high temperature ceramics. To improve the dispersibility of ZrB2, surface preoxidation was developed. After preoxidation, a layer of oxides composed of ZrO2 and B2O3 formed on particle surfaces. The dispersibility of ZrB2 particles in aqueous medium was investigated using zeta potential measurements, sedimentation tests and viscosity measurements. The surface oxygen of ZrB2 particle preoxidised at 800°C was 2·66±0·12 wt-%. It was found that ZrB2 had the best dispersibility and the lowest viscosity after surface preoxidation at 800°C for 1 h.

High Temperature Flexural, Tensile Strength and Oxidation Behavior of Ti3SiC2 Ceramic at 900°C–1300°C in Ambient Air

High temperature flexural and tensile strength of hot-pressed Ti3SiC2 ceramic were measured and analyzed from 900 to 1300°C in ambient air atmosphere. The high temperature flexural and tensile strength are strong functionals of temperature. With the temperature increasing, the high temperature flexural and tensile strength decrease correspondingly. Moreover, the transition from brittle to plastic deformation was observed for both flexural and tensile testing. The oxidation behavior and oxidation mechanism were investigated.