Measurement of interfacial residual stress in SiC fiber reinforced Ni-Cr-Al alloy composites by Raman spectroscopy

Raman spectroscopy was used to measure Raman spectra of the inner SiC fibers and surface C-rich layers of SiC fibers, composite precursors and SiCf/Ni-Cr-Al composites. The residual stresses of the inner SiC fibers and surface C-rich layers were calculated, and the effect of the(Al + Al_2O_3) diffusion barrier layer on the interfacial residual stress in the composites was analyzed in combination with the interface microstructure and energy disperse spectroscopy(EDS) elements lining maps. The results show that the existence of(Al + Al_2O_3) diffusion barrier improves the compatibility of the SiCf/Ni-Cr-Al interface,inhibits the adverse interfacial reaction, and relieves the residual stress inside SiC fibers and at the interface of composite material. Heat treatment can reduce the residual stress at the interface. As the heat treatment time increases, the residual stress at the interface decreases.

An effective strategy towards construction of CVD SiC fiber-reinforced superalloy matrix composite

In this work,a modified approach for preparing CVD SiC fiber-reinforced superalloy matrix composites was rationally developed.The composites were fabricated by vacuum hot pressing(VHP)process using precursor wires coated with(Al+Al2O3)diffusion barrier layers and GH4169 superalloy coatings.BNi-7 brazing filler metals were introduced on the surface of precursor wires in order to decrease the temperature of the VHP process.It was found that the VHP temperature was reduced by about 100℃,and the melting,diffusion,nucleation and growth processes of BNi-7 fillers at 900?C motivated the recrystallization and plastic flow of the matrix under the increasing pressure,thereby a compact composite composed of intact SiC fibers and fine equiaxial grain structure superalloy matrix was achieved.Meanwhile,the elements were distributed homogeneously among the fibers in the composite and no interfacial reactions occurred.This method provides a new insight for designing and manufacturing high-quality composites in practical engineering.

Reconstructing avascular necrotic femoral head through a bioactiveβ-TCP system:From design to application

A variety of techniques have been used for treating avascular necrosis of the femoral head(ANFH),but have frequently failed.In this study,we proposed aβ-TCP system for the treatment of ANFH by boosting revascularization and bone regeneration.The angio-conductive properties and concurrent osteogenesis of the highly interconnected porousβ-TCP scaffold were revealed and quantified through an in vivo model that simulated the ischemic environment of ANFH.Mechanical test and finite element analysis showed that the mechanical loss caused by tissue necrosis and surgery was immediately partially compensated after implantation,and the strength of the operated femoral head was adaptively increased and eventually returned to normal bone,along with continuous material degradation and bone regeneration.For translational application,we further conducted a multi-center open-label clinical trial to assess the efficacy of theβ-TCP system in treating ANFH.Two hundred fourteen patients with 246 hips were enrolled for evaluation,and 82.1%of the operated hips survived at a 42.79-month median follow-up.The imaging results,hip function,and pain scores were dramatically improved compared to preoperative levels.ARCO stage II disease outperformed stage III in terms of clinical effectiveness.Thus,bio-adaptive reconstruction using theβ-TCP system is a promising hip-preserving strategy for the treatment of ANFH.

Effects of Cr and Al Contents on the Preparation of SiC Fiber-Reinforced NiCrAl Alloy Matrix Composite

In this work,the effects of Cr and Al contents on the preparation of SiC fiber-reinforced NiCrAl alloy matrix composites(SiCf/Ni-20Cr-5Al,SiCf/Ni-15Cr-5Al,SiCf/Ni-10Cr-5Al and SiCf/Ni-10Cr-3Al)were thoroughly discussed.The composites were prepared by vacuum hot pressing process using matrix-coated fibers.It was found that Cr solute atoms played a significant role in retarding the recrystallization of NiCrAl alloy matrix,and the Al elements in the form of γ'-Ni3Al phase had a suppression effect on the plastic flow of the matrix.Therefore,the reduction in Cr and Al contents was conductive to the recrystallization and plastic flow of NiCrAl alloy matrix,thereby reduced the size and number of micro-voids in the composite.In addition,this work provides some guidance for designing and manufacturing reasonable SiC fiber-reinforced Ni alloy matrix composites.