As interfaces play a more important role in high-volume-fraction ceramic/metal composites because of containing more hetero-phase interfaces, it is a great challenge to control the interfaces in such composites to balance their strength and plasticity and to obtain high performances. In this work, 50–60 vol% (TiC + TiB2)/Al composites were fabricated in Al–Ti–B4C system via a one-step method of reaction and densification, and their interface bonding and mechanical properties were compared with those of in-situ TiC/Al composites. Apparently, the defects, such as interfacial discontinuity, macro-pores, coarsening and agglomeration of particles, caused by increased ceramic content in the TiC/Al composites, are eliminated in the (TiC + TiB2)/Al composites using Al–Ti–B4C system. The 60 vol% (TiC + TiB2)/Al composite exhibits significantly enhanced mechanical properties, i.e. 70.5%, 60.7% and 69.8% respectively higher yield strength, ultimate compressive strength and plastic strain than 60 vol% TiC/Al composite. Such enhanced mechanical properties are attributed to the improvement in interface bonding strength and therefore the increase in the energy dissipation of crack propagation. The formation of enhanced interface in the (TiC + TiB2)/Al composites results from the reduction in the reaction heat in the Al–Ti–B4C system, improved crystallographic match and improved adhesion work between ceramic particles and matrix. This work may provide a new idea for the design and control of interfaces in high-volume-fraction ceramic-metal composites.

Interface formation and bonding control in high-volume-fraction (TiC+TiB2)/Al composites and their roles in enhancing properties

316L austenitic stainless steel has a wide range of industrial applications. However, one of the major drawbacks is its low yield strength (170–300 MPa in annealed state). We report a method to strengthen 316L by adding 1 wt% and 3 wt% micron-sized TiC particles using low energy ball milling for the powder feedstock preparation followed by selective laser melting (SLM). The TiC particles were observed to be uniformly dispersed and well bonded to the 316L matrix after SLM. The 316L-TiC composites obtained were close to full density and the austenite grains were significantly refined with the addition of TiC particles. Tensile tests show that adding 1 wt% and 3 wt% TiC particles leads to a significantly increased yield strength (660 MPa and 832 MPa) and UTS (856 MPa and 1032 MPa) and maintains the good ductility (55% and 29% elongation). These findings offer a new perspective on the strengthening of 316L stainless steel

Selective laser melting of dispersed TiC particles strengthened 316L stainless steel

Poor mechanical strength and creep resistance limit the orthopedic application of biodegradable Zinc (Zn). In present work, cerium (Ce) was alloyed with Zn using laser additive manufacturing technique. As one kind of rare earth element, Ce possessed high surface activity, which effectively interrupted the grain growth and caused the formation of stable intermetallics, thus contributing to grain refinement strengthening and precipitate strengthening. More significantly, Ce alloying activated more pyramidal slip by means of reducing the critical resolved shear stress during plastic deformation, and resultantly formed the sessile dislocations, which caused the accumulated strain hardening and improved the creep resistance. As a result, Zn-Ce alloy exhibited a considerably improved ultimate tensile strength of 247.4 ± 7.2 MPa, and a reduced creep rate of 1.68 × 10−7 s−1. Moreover, it exhibited strong antibacterial activity, as well as favorable cytocompatibility and hemocompatibility. All these results demonstrated the great potential of Zn-Ce alloy as a candidate for bone repair application.

Rare earth improves strength and creep resistance of additively manufactured Zn implants

Although laser powder bed fusion (LPBF) can produce complex structures with promising properties, there still exists a concern on the diversity in materials, especially composites, for LPBF. This work innovatively used NiTi and Nb powders to prepare NiTi–Nb eutectic-type alloy by LPBF, which provides a new method to prepare NiTi–Nb shape memory alloy and could be an alternative for tailoring microstructure. The semi-molten Nb particle phase was retained during LPBF, so that β-Nb and the eutectic structure display a gradient distribution in the Nb diffusion concentration. The heat treatment process (annealed at 850 °C for 0.5 h) makes NiTi–Nb samples have high yield strength (~1640 MPa), high compressive strength (~2380 MPa), and high compressive strain (~39%), which are superior to the corresponding ones of its as-built and as-cast counterparts. Large Nb phase particles with a size of 10–30 μm are retained and accelerated the formation of eutectic phase and β-Nb precipitate phase. Overall, the presence of β-Nb phase has a beneficial effect on the alloy, and a large number of intertwined dislocations and stacking faults around the β-Nb phase promote the formation of martensite under stress loading. The eutectic phase makes an important contribution to the high strength and plasticity of the NiTi–Nb alloy.

Strengthening mechanism and micropillar analysis of high-strength NiTi–Nb eutectic-type alloy prepared by laser powder bed fusion

Grain refinement and crack inhibition of hard-to-weld Inconel 738 alloy by altering the scanning strategy during selective laser melting

Characterization of nanoparticle mixed 316 L powder for additive manufacturing

In this work, strengthening of 316L stainless steel was achieved through addition of 1 and 3 wt% TiC nanoparticles. The TiC nanoparticles and 316L powders were mixed using low energy ball milling and then processed by selective laser melting. The grains are significantly refined from 16.8 μm to 6.9 μm with the addition of 3 wt% TiC nanoparticles. Addition of 1 and 3 wt% TiC nanoparticles remarkably increased yield strength (694 MPa and 773 MPa) and ultimate tensile strength (888 MPa and 988 MPa). Meanwhile, the tensile elongation was kept at a high level (47% and 32%). The strength enhancement primarily results from Orowan strengthening by the nanoparticles, and the reduction of ductility is related to the suppression of twinning induced plasticity. 

Grain refinement and strengthening of 316L stainless steel through addition of TiC nanoparticles and selective laser melting

γ-TiAl-based alloys have been studied for decades due to their attractive properties. However, the applications are limited because of their poor formability. Electron beam melting (EBM) is advanced in fabricating components with high complexity. Studies have shown that γ-TiAl alloys can be successfully fabricated using EBM. To further explore the advantages of EBM, a bimetal component is designed: a turbine blade that containing an EBM-built Ti–48Al–2Cr–2Nb blade and a Ti–6Al–4V fir tree mount. The Ti–48Al–2Cr–2Nb side is directly built using EBM on a wrought Ti–6Al–4V substrate. Different printing strategies are applied in order to generate straight and curved diffusion interlayers. No defect is observed in both of the EBM built parts and the interlayer zones. The interlayers consist of α2-Ti3Al and B2 phases. To evaluate the reliability of the bimetal component, the tensile strength of the bimetal component is assessed. The sample with a curved interlayer exhibits a higher strength than that with a straight interlayer. The average tensile strength of the samples with curved interlayer reachs 389 MPa, which is much higher than that of the brazed TiAl/Ti–6Al–4V joints. The tensile test reveals that the fracture occurred in the interlayer zone. This work provides a promising application of γ-TiAl based alloys and a new method to form a strong bond for bimetal materials.

Hybrid manufacturing of γ-TiAl and Ti–6Al–4V bimetal component with enhanced strength using electron beam melting

316L stainless steel has a wide range of engineering applications. However, its relatively low yield strength limits its applications. In this work, strengthened 316L stainless steel was fabricated via selective laser melting (SLM) with the addition of 3 wt% micronsized TiC particles. The grains of 316L are significantly refined to approximately 3 μm. Although micronsized TiC particles were used as reinforcement, in-situ formed nanosized TiC particles were observed. Tensile tests were carried out and the yield strength of SLM 316L-3TiC was 803 MPa–832 MPa with the elongation ranging from 25.8% to 28.5% when fabricated with laser power between 225 W and 275 W. Relative to SLM 316L without TiC particles which has a yield strength of 599 MPa, the strength enhancement is found to be 97 MPa from grain refinement and 140 MPa from Orowan strengthening.

Wengang Zhai

Papers

Selective laser melting of dispersed TiC particles strengthened 316L stainless steel

Characterization of nanoparticle mixed 316 L powder for additive manufacturing

Grain refinement and strengthening of 316L stainless steel through addition of TiC nanoparticles and selective laser melting

Hybrid manufacturing of γ-TiAl and Ti–6Al–4V bimetal component with enhanced strength using electron beam melting

In-situ formation of TiC nanoparticles in selective laser melting of 316L with addition of micronsized TiC particles