Sintering behavior and microstructure evolution in cp-titanium processed by spark plasma sintering

Mechanical Properties of Ti-15Mo Alloy Prepared by Cryogenic Milling and Spark Plasma Sintering

Metastable β-Ti alloy Ti-15Mo was prepared by cryogenic ball milling in a slurry of liquid argon. Material remained ductile even at low temperatures, which suppressed particle refinement, but promoted intensive plastic deformation of individual powder particles. Repetitive deformation of powder particles is similar to the multidirectional rolling and resembles bulk severe plastic deformation (SPD) methods. Initial and milled powders were compacted by spark plasma sintering. Sintered milled powder exhibited a refined microstructure with small β-grains and submicrometer sized α-phase precipitates. The microhardness and the yield tensile strength of the milled powder after sintering at 850 °C attained 350 HV and 1200 MPa, respectively. Low ductility of the material can be attributed to high oxygen content originating from the cryogenic milling. This pioneering work shows that cryogenic milling followed by spark plasma sintering is able to produce two-phase β-Ti alloys with refined microstructure and very high strength levels.

Mechanical Alloying and Electrical Current-Assisted Sintering Adopted for In Situ Ti-TiB Metal Matrix Composite Processing

In this work, mechanical alloying and electrical current-assisted sintering was adopted for in situ metal matrix composite material processing. Applied at the initial powder stage, mechanical alloying enables a homogeneous distribution of the starting elements in the proposed precursor powder blends. The accompanying precursor preparation and the structurally confirmed size reduction allow obtainment of a nanoscale range for the objects to be sintered. The nano precursors aggregated in the micro-sized particle objects, subjected to electrical current-assisted sintering, characterize the metal matrix composite sinters with high uniformity, proper densification, and compaction response, as well as maintaining a nanoscale whose occurrence was confirmed by the appearance of the highly dispersed reinforcement phase in the examined Ti-TiB material example. The structural analysis of the sinters confirms the metal matrix composite arrangement and provides an additional quantitive data overview for the comparison of the processing conditions. The mechanical alloying examined in this work and the electrical current-assisted sintering approach allow in situ metal matrix composite structures to create their properties by careful control of the processing steps.