Xiping Cui

Ductile-Phase Toughening in TiBw/Ti-Ti3Al Metallic-Intermetallic Laminate Composites

The concept of ductile-phase toughening was explored in a metallic-intermetallic laminate (MIL) composite comprising alternating layers of Ti3Al and TiBw/Ti. The laminates, in which the TiBw/Ti layers were intended to impart toughness to the brittle Ti3Al, were fabricated in situ by hot pressing and reaction annealing. Compared with monolithic Ti3Al, the MIL composite exhibited marked increases in both fracture toughness and tensile elongation because of stress redistribution and strain delocalization by in situ interfaces.

A novel approach to accelerate the reaction between Ti and Al.

Pure Ti foils and SiCp/Al composite foils were employed to investigate the parabolic growth kinetics of TiAl3 at 660°C. Compared with pure Al foils, the introduction of SiC particles significantly refined TiAl3 grain size by the solid solution of silicon. Corresponding refinement mechanisms were concluded from the perspective of the nucleation of TiAl3. Micromechanics analysis shows that the fine TiAl3 grains own a small viscous resistance, and subsequently an improvement in the reaction rate could be achieved. This meaningful law also applies extensively to Ni/Al and Fe/Al systems.

Effects of rolling deformation on microstructure and mechanical properties of network structured TiBw/Ti composites

TiB whiskers reinforced pure Ti (TiBw/Ti) composites with a novel network microstructure were successfully fabricated by reaction hot pressing (RHP). TiB whiskers are in situ synthesized around the large pure Ti matrix particles, and subsequently formed into TiBw network structure. The novel TiBw/Ti composites with a network microstructure exhibit a superior combination of mechanical properties. In order to further improve the mechanical properties and guide the subsequent plastic forming, the rolling deformation behavior of the novel composites was investigated. The results show that the strength of the novel TiBw/Ti composites can be effectively enhanced by rolling deformation due to the matrix deformation strengthening effect, and increased with increasing the rolling reduction. The strength of 8.5%TiBw/Ti (volume fraction) composite is significantly increased from 842 MPa to 1030 MPa by rolling deformation. It is certain that the TiB whiskers are gradually broken with increasing the rolling reduction, which is harmful to the mechanical properties of the composites.

Formation of intermetallic compound layer in multi-laminated Ni–(TiB2/Al) composite sheets during annealing treatment

Solid-state reactive diffusion between Ni and Al was investigated during annealing at 650°C by employing multi-laminated Ni-(TiB(2)/Al) composite sheets. In multi-laminated Ni-(TiB(2)/Al) composite sheets annealed up to 5min NiAl(3) was the only phase observed in the diffusion zone, and Ni(2)Al(3) appeared after longer annealing time. Most grains of Ni(2)Al(3) showed equiaxed morphology rather than columnar microstructures like NiAl(3), due to the low concentration gradients of Al and Ni at the Ni/NiAl(3) interface. The preferential formation of this intermetallic compound NiAl(3) in multi-laminated Ni-(TiB(2)/Al) composite sheets was predicted using an effective heat of formation model. The present work indicated that both Ni and Al interdiffused, and the formation of NiAl(3) was a reaction-diffusion process.

Solid State Reaction Mechanism and Microstructure Evolution of Ni-Al Powders during High Energy Ball Milling Revisited by TEM

Microstructure evolution during the formation of B2-NiAl by high energy ball milling of equiatomic elemental mixtures was studied by X-ray diffractometer, scanning electron microscopy, and transmission electron microscopy (TEM). The crystallite size, lattice defects and ordering of the B2-NiAl were monitored via TEM as function of milling time. The diffusion reaction, Ni+Al→NiAl3 or/and Ni2Al3, occurred during high energy ball milling, and to a certain extent offered the stored energy for the explosive exothermic reaction, Ni+Al→B2-NiAl. The fine microstructure of newly formed B2-NiAl after 5 h milling involved high density defects, e.g. antiphase boundary, long range ordering domains, vacancies, and dislocations.

Influence of plastic strain localisation on the mechanical properties of metal matrix composites

Abstract The aim of the present study is to reveal the most critical underlying factor influencing the mechanical properties of metal matrix composites (MMCs). It is shown that the mechanical properties of MMCs are essentially governed by the degree of strain localisation during plastic deformation. In other words, the MMCs exhibit superior mechanical performance only if the strain localisation is obviously inhibited and the accumulated stresses can be effectively transferred out. The work provides a new perspective in guiding the design of next-generation high-performance MMCs by suppressing the strain localisation as far as possible.

Tensile Fracture Characteristics Along Different Directions of Laminated Ti-TiBw/Ti Composites with Two-Scale Hierarchical Structures Fabricated by Reaction Hot Pressing

The tensile behaviors and fracture characteristics of laminated Ti-TiBw/Ti composites with two-scale hierarchical structures along different directions were investigated in detail. The laminated Ti-TiBw/Ti composites exhibited the highest tensile strength and fracture elongation along the longitudinal direction. Multi-necking and interfacial “intercrystalline-like” network fracture dominated the fracture behaviors along the transversal direction, which are attributed to the high strain (\( \mathop \varepsilon \nolimits_{\text{Ti}} \)), low strain hardening exponent (\( \mathop n\nolimits_{\text{Ti}} \)) of Ti layer, and obvious strain misfit at the interface, respectively. The longitudinal fracture characteristics of laminated Ti-TiBw/Ti composites reveals diffuse necking delaying, localized shear band transferring, tunnel cracks blunting, micro-cracks insensitivity, crack bifurcation and interfacial delamination absenting phenomena, which are beneficial to the toughening the laminated composites.

Microstructure and Reaction Mechanism of Multi-Laminated Ti-(SiCp/Al) Composites Subjected to Annealing at 1300°C

The multi-laminated Ti-(SiCp/Al) composite was produced by hot press and subsequent hot roll bonding of Ti and SiCp/Al foils. The microstructure evolution of the composite in reaction annealing was investigated by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectrometer (EDX) and X-ray diffractometer (XRD). The results show that after the reaction annealing at 1300°C for 3h, the Ti and SiCp/Al foils were completely consumed and transformed into the TiAl composite with a microlaminated structure. The microlaminated microstructure of the composite is composed of Ti3Al/(TiAl+Ti5Si3p)/Ti5Si3/duplex-phase (TiC+Ti3AlC) layers. The reaction mechanism is elucidated by employing the reaction model.