No abstract

Recently, pulsed lasers have demonstrated great potential in targeted synthesis in solution based nanomanufacturing, realizing high precision and accuracy in space, time and energy input. The unique temperature history induced by pulsed lasers is indispensable to understand the related fundamentals and to realize the precision control of deposition. In this study a heat transfer model was developed and applied to predict the temporal evolution and the spatial distribution of pulsed laser induced temperature change across the reaction sites. Chemically deposited ZnO crystals were studied as an example, showing the relationships among laser parameters and heating conditions, and deposited crystal characteristics. Peak temperature and heat accumulation induced by pulsed laser were found to affect deposited crystal number density and size. The nucleation number density distribution was found to be correlated with the spatial temperature distribution and inversely proportional to the crystal size. The presented heat transfer model is a crucial tool to understand crystallization fundamentals and it is essential for facilitating pulsed laser as a new tool for research, design, manufacturing and control.

There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material from the bottom up. It has the distinct advantages of low preparation costs and a high geometric creation capability. However, the wide range of industrial processing conditions results in large variations in the fatigue lives of metal components fabricated using AM. One of the main reasons for this variation of fatigue lives is differences in microstructure. Our methodology incorporated a crystal plasticity finite element model (CPFEM) that was able to simulate a stress–strain response based on a set of randomly generated representative volume elements. The main advantage of this approach was that the model determined the elastic constants (C11, C12, and C44), the critical resolved shear stress (g0), and the strain hardening modulus (h0) as a function of microstructure. These coefficients were determined based on the stress–strain relationships derived from the tensile test results. By incorporating the effect of microstructure on the elastic constants (C), the shear stress amplitude (Δτ2) can be computed more accurately. In addition, by considering the effect of microstructure on the critical resolved shear stress (g0) and the strain hardening modulus (h0), the localized dislocation slip and plastic slip per cycle (Δγp2) can be precisely calculated by CPFEM. This study represents a major advance in fatigue research by modeling the crack initiation life of materials fabricated by AM with different microstructures. It is also a tool for designing laser AM processes that can fabricate components that meet the fatigue requirements of specific applications.

Laser-induced chemical solution synthesis has been recently developed as a new generic method to create porous nanostructured materials for complex and miniaturized devices. The material made by this approach is successfully demonstrated for electrochemical catalytic, nanoscale powders, protective coatings, and other applications. One question has therefore been raised: What are the mechanical properties of the porous materials deposited by the laser-induced chemical solution synthesis? This paper has attempted to explore the mechanical properties of such porous nanostructured materials deposited by this new nanomanufacturing method. This process also offers an innovative opportunity to study the strength of a very simple bonding in additive manufacturing. A thin-film of copper nanoparticles is deposited on copper substrates; then, the microstructure of the deposited film is characterized by scanning electron microscope (SEM), and mechanical properties are investigated by a variety of experiments, such as microhardness test, nano-indentation test, bending test, and adhesion test. The mechanical properties of substrates with surface deposition have been shown to have adequate bond strength (>60 g/mm) to allow effective usage in intended applications. Based on the test results, statistical regression and significant tests have also been carried out. A new model for the nano-indentation of the porous coating (film) is proposed. The empirical results have shown that the effect of coating thickness is more prominent on mechanical properties in the case of thick coating deposition.

Temperature history prediction is essential for a better understanding of the relationship between microstructural change and processing conditions for energy beam additive manufacturing fabricated components. Here, a new efficient approach combining a moving heat source analytical model with a melting and solidification model is presented. An innovative method is proposed to compute the “effective computation zone” as boundary condition, which can save the computation time significantly. Notably, the computational efficiency can improve by 10^4 to 10^5 compared with finite element models. With this range of improvement efficiency, the temperature predicted based on this method is consistent (around 9% of average deviation) with experimental measurements by thermocouple. This model can be used as a reference to define the boundary condition for further complex numerical analysis with improved accuracy at a reduction of efficiency as desired. In addition, it can be used as a reference to determine processing conditions that would allow the efficient and effective control of the temperature history within a range for a certain microstructure design.