Abstract
Ti-based metal matrix composites (MMC) represent an alloy class with highly desired performance, but implementation has been hindered by poor processability. It is now recognized that MMCs can be formed in-situ through exploitation of the rapid cooling rates of laser powder bed fusion (LPBF) and targeting invariant reaction compositions to minimize the propensity for solidification cracking. Laser line scans and surface remelts of Ti-C, Ti-B, Ti-Si, and Ti-Fe eutectic compositions, and ternary Ti-Si compositions plus C/Zr and quaternary Ti-Si-Zr plus Al/Sn, were performed to assess potential material amenability to the LPBF process at low-cost as well as determining the nanostructure and hardness properties. These base compositions were selected to compare (i) typical interstitial elements and substitutional elements, (ii) increasing element additions, and (iii) α and β stabilizing elements. A hyper-eutectic Ti-15Si wt.% alloy was also fabricated and demonstrates the benefit of near eutectic compositions on processability. Hot-cracking is observed in Ti-Fe following surface remelts while the eutectic C, B and Si containing MMCs appear to be amenable to LPBF. Atom probe tomography and scanning electron microscopy reveal a nanocellular structure of Ti matrix with intercellular Ti5Si3 within the Ti-15Si wt.% sample; the Ti-Si ternary and quaternary compositions exhibit similar cellular nanostructure. The β matrix is retained on laser remelting of Ti-Fe, as well as all Zr-containing samples, with α + β present in the Ti-Si-Zr-Al sample. Exceptional hardness values are obtained across the MMCs, highlighting very promising material systems that may be processable via LPBF with future development.