The research goal of the project is to investigate laser shockwave compaction of nanoscale powders for developing a novel additive manufacturing process, designated as Shock Wave Induced Freeform Technique (SWIFT) that will be superior to the existing additive manufacturing processes such as selective laser sintering (SLS) in performance, quality and hard tooling capability. The objectives of SWIFT are to: 1) manufacture high performance diamond micro-tools composed of nanodiamond particles with high aspect ratios, smooth surfaces and sharp edges; 2) explore the physics underlying the SWIFT technology for optimizing the manufacturing process.

Extensive experiments and molecular dynamics simulation have been conducted to study the material processing using SWIFT. For experiment, the wear and lifetime of tools coated with diamonds using the shockwave sintering have been studied. Scanning electron microscope analysis of worn-tools revealed that different wear mechanisms are associated with coated and uncoated tools. In the case of uncoated tools, large amount of wear debris and deformation are readily seen. The dominated wear mechanism is adhesion and material dissolution, as well as chipping and plastic deformation due to mechanical shock and thermal fatigue, especially the high positive rake angles of this carbide insert can also contribute to chipping. For nanodiamond doped worn-tool, it is clearly seen that adhesion and material dissolution was stopped by diamond enforcement phase. Microscope images of flank wear and crater wear show that worn condition is much more serious for uncoated tool, and the flank face is pretty rough due to adhesion and material cold welding. For nanodiamond doped tool, flank wear is low and smooth, which can be explained that the high hardness of diamond withstood the high stresses developed in the cutting zone and rapid heat dissipation of diamond resisted the dissolution of WC in aluminum. The similar phenomenon was also observed in crater wear. Based on the SWIFT concept, a new additive manufacturing process has been developed for hard tooling via experimental and computational techniques. The sacrificial layer overlay plays an important role in this additive manufacturing process to generate a strong shock wave for particle compressing.

Our atomistic level modeling shows that under high compressive stress effect, nanoparticles experienced very strong interaction and grow to a bulk material without real melting. This proved the feasibility of the shockwave cold sintering process. A new physical model has been developed to characterize the nanocrystalline structure after shock wave compressing. This model worked very well to identify the material twisting and melting. Pioneering and systematic studies have been carried out to study the material behavior under shock wave formation and effect, as well as the phase change behavior in extremely confined domains. The uncovered lifetime of voids under the effect of shock wave provides important guidelines for future technology development and laser parameter optimization.

This project has provided extensive training to four Ph.D. students. Three of them have defended their Ph.D. dissertation successfully. During the period of the project, we have provided extensive research training to six undergraduate students. Under the support of this project, 9 papers have been published in highly visible journals. Also we have disseminated the results at two international conferences.

Last Modified: 11/13/2015
Modified by: Xinwei Wang