The objective of this study was to quantitatively investigate the build-up of residual stresses in selective laser-melted 316L stainless steel samples and identify the nature of the stresses. In addition, the effectiveness of stress relief heat treatment in reducing residual stresses or changing their characteristics was examined. The results were compared against those obtained from conventionally hot-rolled 316L samples.

Spattering is an unavoidable phenomenon in the selective laser melting (SLM) process, which can cause various printing defects and harmful powder recycling. Since the size of powder spattering is too small at the micron level, it is difficult to investigate the entire dynamic spattering process experimentally. The comprehensive understanding of the intricate dynamics of powder spattering during the SLM process remains incomplete. Therefore, we develop a new multiphase flow model to study the transient dynamic behaviors of the gas phase and powder spattering, which agrees well with the experimental observation result. It is the first time that the whole transient dynamic process of powder motion from starting to move induced by the vapor jet to falling to the substrate wall and stopping completely was observed. Powder spattering motion dynamics induced by metal vapor jet and argon gas flow, as a function of time, laser parameters, and location, are presented. The moving speed, total amount, and dropping distribution on the substrate of powder spattering that varies with laser parameters are quantified.

Amorphous alloys have attracted extensive attention due to their unique atomic arrangement and excellent properties. However, the application in practical engineering is seriously limited due to the size, crystallization and other problems. Laser additive manufacturing technology has the characteristics of high heating, cooling rate and point by point melting deposition, which provides a new idea for the preparation of amorphous alloys. Zr 50 Ti 5 Cu 27 Ni 10 Al 8 amorphous alloy was prepared on the surface of pure zirconium substrate by selective laser melting technology. The composition and structure of the samples were characterized. The results show that the samples are mainly composed of amorphous phase, and the crystallization mainly occurs in the superimposed zone of heat affected zone. With the decrease of laser power, the area of crystallization zone and the number of crystallization particles decrease. However, if the laser power is too low, there will be non-fusion defects and cracks, which will seriously affect the forming quality and amorphous rate of amorphous alloy.

The product quality of selective laser melting (SLM) is closely related to the alloy powder characteristics, including the size distribution and the oxygen content. In this work, the 316L stainless steel powder was prepared by a vacuum atomization furnace and sieved into a normal-sized distribution range from 15 to 53 μm with a median diameter of 37.4 μm, and a fine-sized distribution range from 10 to 38 μm with a median diameter of 18.9 μm. Then they were mixed with each other in different proportions. The results show that, under the condition of the same SLM parameters, the SLM part, with adding a large amount of fine-sized powder, has a lower density and strength, as well as more holes and spheroidized particles, compared with the SLM part with adding a small amount of finer-sized powder. Furthermore, the 316L stainless steel powder with a high oxygen content was prepared by a non-vacuum atomization furnace. Although the 316L stainless steel powder with a high oxygen content can be evenly spread in the SLM process, the surface layer of the powder is easy to form an oxide film during the cooling and solidification of powder inside the molten pool. Under the action of thermal stress, the small crack forms and expands along the oxide film, eventually leading to large cracks inside the melt channel.

In this study, WC-Co coatings were deposited on additively manufactured 316L stainless steel substrates by HVOF spraying. Prior to spraying, the SLM parts were exposed to various mechanical pretreatments, before and after which their surface topography and residual stress state were assessed. After spraying, Vickers indentation tests were conducted to assess interfacial bond strength between the coating and substrate. To differentiate between topographical effects and residual stress related phenomena, stress-relief heat treatments were conducted at various points in the investigation.

In this work, a novel additive manufacturing process was proposed and employed in the production of stainless steel components. The underlying concept is to use selective laser melting (SLM) to fabricate a core structure onto which basic features are added by cold spraying (CS), followed by heat treatment and finish machining. The microstructure and mechanical properties of as-fabricated and heat-treated parts were studied, and interfacial bonding between the SLM core and a typical CS feature was assessed. In the as-fabricated state, it is observed that the CS material has a dendritic structure similar to the feedstock, while the SLM core is characterized by cellular subgrains confined in coarse grain structures. Following heat treatment, interparticle boundaries are less well defined, equiaxed coarse grains and twinning appear, and the extremely fine subgrains in the SLM material are enlarged. Heat treatment is also shown to improve tensile strength in the CS material and interfacial bond strength between the CS features and SLM core.

In this work, a 2D axisymmetric model of gas atomization at unsteady state that accounts for break-up and solidification is used to simulate laser melting of gas atomized powder. With an optimal nozzle width of 0.6-1 mm and a nozzle angle of 30-32°, the yield of fine 15-45 μm stainless steel powder, suitable for selective laser melting, is shown to increase from 20% to 35%. The effect of laser power on the melting channel width, microstructure, and mechanical properties of the sample is also investigated.

Additive manufacturing (AM) has already been evolved into a promising manufacturing technique. In order to achieve the performance of conventionally manufactured components, additively manufactured components must meet at least the same mechanical and physical requirements. Due to the layer-wise building process, the properties of additively manufactured components differ from that of bulk materials. Within the scope of this study, selective laser melting (SLM) was employed to manufacture specimens which serve as substrates for a subsequent coating process. An Inconel 718 (IN718) alloy served as AM feedstock. Mechanical posttreatments were applied to the AM samples and rated with respect to the successive thermal spraying process. The produced AM samples were examined in their initial state as well as under post-treated conditions. In this report, the resulting surface roughness was analyzed. Different AM samples were coated by means of high velocity oxy-fuel (HVOF) spraying and atmospheric plasma spraying (APS). The interface between the thermally sprayed coating and the AM substrate was metallographically investigated. Adhesion tests were conducted to scrutinize the bond strength of the coating to the AM substrate.

Metal and polymer additive manufacturing is advancing on several applications. On the other hand, materials cermet such as WC/Co for functional structure molding by additive manufacturing are under studying. There are few reports for WC cemented carbide additive manufacturing process by forming with polymer binder then sintering. This indirect process has difficulties to make high precision functional parts due to shape control during additional sintering process. Direct forming is desired for high precision parts. However, factors and/or mechanism to achieve direct formed functional structure have been unclear in many aspects. In this study, the process conditions of the direct selective laser melting were investigated to achieve dense and hard WC cemented carbide mold parts. The optimization of laser melting conditions for WC/Co agglomerated and sintered powder was examined. In order to forming a dense and high hardness parts, the optimum conditions between powder preparation and laser energy density which related with laser power, scan speed and spot diameter were appeared by this experiments. Moldings more than 1500HV are achieved at low laser energy density. However, some of pores were observed in moldings. In addition, the dense molding could be obtained by high laser energy density. This means optimum dense functional WC cemented carbide molding is available by optimization of the molding condition. It is applicable for growing industries like automotive, aviation and cutting tool.

Tungsten carbide (WC) is a well-known material used to increase the wear resistance of iron-based composite materials that exhibit a favorable wettability with iron alloy particles. In this work, two different additive manufacturing technologies, i.e., cold-spray additive-manufacturing (CSAM) and selective laser melting (SLM), were used to fabricate WC/maraging steel 300 (WC/MS300) composites. An investigation comparing the microstructure and tribological behaviors of the composites was carried out. In addition, the evolution of the reinforcement phase during these two processes was characterized by SEM and EDS methods.

Directed light fabrication (DLF) is a rapid fabrication process that fuses gas delivered metal powders within a focal zone of a laser beam to produce fully dense, near-net shape, 3D metal components from a computer generated solid model. Computer controls dictate the metal deposition pathways, and no preforms or molds are required to generate complex sample geometries with accurate and precise tolerances. The DLF technique offers unique advantages over conventional thermomechanical processes or thermal spray processes in that many labor and equipment intensive steps can be avoided to produce components with fully dense microstructures. Moreover, owing to the flexibility in power distributions of lasers, a variety of materials have been processed, ranging from aluminum alloys to tungsten, and including intermetallics such as M05Si3. Since DLF processing offers unique capabilities and advantages for the rapid fabrication of complex metal components, an examination of the microstructural development hhas been performed in order to define and optimize the processed materials. Solidification studies of DLF processing have demonstrated that a continuous liquid/solid interface is maintained while achieving high constant cooling rates that can be varied between 10 to 10 5 Ks-1 and solidification growth rates ranging up to 10-2 ms-1.

The Directed Light Fabrication (DLF) process uses a laser beam and metal powder, fed into the laser focal zone, to produce free-standing metal components that are fully dense and have structural properties equivalent to conventional metal forming processes. The motion of the laser focal zone is precisely controlled by a motion path produced from a 3-dimensional solid model of a desired component. The motion path commands move the focal zone of the laser such that all solid areas of the part are deposited and the part can be built (deposited) in its entirety to near net shape, typically within +/-0.13mm. The process is applicable to any metal or intermetallic. Full density and mechanical properties equivalent to conventionally processed material are achieved.