No abstract

Three kinds of Bi-based solder powders with different chemical compositions of binary Bi-Sn, ternary Bi-Sn-In, and quaternary Bi-Sn-In-Ga were prepared using a gas atomization process and subsequently ball-milled for smaller-size fabrication. In particular, only the quaternary Bi-Sn-In-Ga solder powders were severely broken to the size of less than 10 µm in a polyhedral shape due to the presence of the constitutional element, the degree of overall oxidation, and the formation of solid solution, which had affected the fractured extent of the Ga-containing solder powders. Furthermore, a melting point also decreased by the addition of In and/or Ga into the binary Bi-Sn solder system, resulting in a melting point of 60.3˝C for the Bi-Sn-In-Ga solder powders. Thus, it was possible that fractured Bi-Sn-In-Ga solder powders were appropriate for the adhesion of more compact solder bump arrays, enabling reflowing at the low temperature of 110˝C on a flexible polyethylene terephthalate (PET) substrate.

This paper demonstrates the successful printing of H13 tool steel by a selective laser melting (SLM) method at a scan laser speed of 200 mm/s for the best microstructure and mechanical behavior. Specifically, the nanoindentation strain-rate sensitivity values were 0.022, 0.019, 0.027, 0.028, and 0.035 for SLM H13 at laser scan speeds of 100, 200, 400, 800, and 1600 mm/s, respectively. This showed that the hardness increases as the strain rate increases and, practically, the hardness values of the SLM H13 at the 200 mm/s laser scan speed are the highest and least sensitive to the strain rate as compared to H13 samples at other scan speeds. The SLM processing of this material at 200 mm/s laser scan speed therefore shows the highest potential for advanced tool design. Residual stress is expected to affect the hardness and shall be investigated in future research.

Nano-mechanical properties of selective laser melted H13 steel at a scan laser speed of 100 mm/s were investigated using nanoindentation tests. The findings shed light on the interrelationship between the nanoindentation strain rate and hardness. It was found that the strain-rate sensitivity exponent (m = 0.022) of this material indicated that the nanoindentation hardness increased in a range of (8.41 to 9.18) GPa with an increase in the strain rate ranging from 0.002 to 0.1 s−1.