# Study of the Microstructure Characterization and In Situ Observation of Crack Propagation in TC4/Al3Ti Metal–Intermetallic Laminated Composites

## TL;DR

This study examines the microstructure and crack behavior in TC4/Al3Ti metal composites to understand how their structure affects toughness and fracture resistance.

## Contribution

The paper introduces in situ observation techniques to analyze crack propagation and microstructural characteristics in metal–intermetallic laminated composites.

## Key findings

- TC4/Al3Ti interfaces show good bonding and wavy morphology with Kirkendall pores in the Al3Ti layer.
- Fracture resistance is enhanced through crack deflection, blunting, and plastic deformation in TC4 layers.
- GND density is higher in TC4 layers (2.53 × 10^14 m−2) compared to Al3Ti layers (1.74 × 10^14 m−2).

## Abstract

TC4/Al3Ti metal–intermetallic laminated (MIL) composites were fabricated by the vacuum hot-pressing process at 650 °C. The microstructure characteristics, i.e., grain boundary distribution, crystallographic orientation and Kernel Average Misorientation (KAM) map, were analyzed using EBSD. Meanwhile, the distribution of local strain and the fracture behavior of TC4/Al3Ti MIL composites during tensile process were determined by Digital Image Correlation (DIC) and in situ tensile experiments, respectively. Results show that the TC4/Al3Ti interfaces are well bonded and exhibit a distinct wavy morphology. The obvious Kirkendall pores and centerline are observed within the central region of the Al3Ti layer. The texture components of (10-10) <0001> and (11-20) <10-10> are predominant in the TC4 layers; (100) <001> and (110) <001> are observed in the Al3Ti layer. Additionally, the average geometrically necessary dislocation (GNDs) density is 2.53 × 1014 m−2 in the TC4 layer, whereas it is 1.74 × 1014 m−2 in the Al3Ti layer. In the tensile test, the fracture resistance of TC4/Al3Ti MIL composites is significantly improved by the plastic deformation of the TC4 layers and the suppression of crack-tip instability. It is found that the extrinsic toughening mechanisms contain crack deflection, crack blunting, crack bridging, multiple cracking modes, and the plastic deformation of ductile TC4 layers in TC4/Al3Ti MIL composites. The real-time observation technique may provide more complete insights into the relationship between fracture behavior and enhanced toughness.