Journal des lasers, optiques et photoniques

Microstructural and Geometric Characteristics Investigation of Laser-Aided Direct Metal Deposition

Abstract

Reza Shoja Razavi

Direct Metal Deposition (DMD) is a metal deposition technique, which is well- known for high-quality and high-productivity level of fabrication. In the current economic situation with worldwide trend for developing new products, the importance of time and cost reduction increases day-by-day. To achieve this goal the man-machine-material interaction should be maximized. Direct Laser Metal Deposition (DLMD) is one of the most famous approaches for this. DLMD is one kind of 3D printing technology (additive manufacturing) together with laser cladding process. In DLMD, it is possible to fabricate fully functional metallic parts directly from CAD data, which involves a feeding of metal powders through a nozzle into a high power laser beam and creates a melt pool on the surface of the solid substrate upon which a metallic powder is injected. DLMD process are now acknowledged worldwide and is also known to all by several other names such as Laser Metal Deposition (LMD), Direct Laser Deposition (DLD), Laser Engineered Net Shaping (LENS), Direct Light Fabrication (DLF), Laser Deposition Welding (LDW) and Powder Fusion Welding (PFW). After development of this process in 1995, lot of researchers for several years work on various aspects of high quality deposition with dimensional accuracy such as good clad geometry, clad height, and microstructure study of the mechanical properties. An attempt has been made to focus on proper selection of the set up configuration for direct laser metal deposition to fulfill the requirement and help to achieve high quality deposition. Empirical-statistical models have been produced since the advent of LDMD as they avoid the complexity of analyzing the physical phenomena of the process itself. Direct metal deposition is typically described as having three “primary” process inputs of laser power, powder mass flow rate, and traverse speed. Most models have concentrated on relating these to final track geometry, typically using regression methods to relate input and response variables. Permitting materials to grow along specific orientation by means of directional solidification technique can optimize their structural or functional properties. Ni-based super alloys are the preferred material for turbine blades given their high temperature strength, microstructural stability, and corrosion resistance. Casting methods have been improved from conventional investment casting, which produces an Equiaxed (EQ) grain structure, to Directional Solidification (DS), which produces Columnar-Grain (CG) and Single Crystal (SC) structures. Although polycrystalline Ni-based super alloys are inherently strong, their properties can be further improved through processing. Ensuring crystal cohesion during solidification by avoiding the formation of cracks and pores is a major challenge in materials science. Under others, the safety of gas turbine components and of laser welds for the aerospace and automotive industries depends on it. Solidification cracking (also called hot cracking or hot tearing) is characterized by extended openings that form during solidification in the mushy zone.