Search Results for selective laser melting

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.

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.

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.

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.

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.

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.

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.

Cold spraying has great potential for additive manufacturing, especially of oxidation-sensitive metals, because the material is not melted and significantly higher deposition rates can be achieved than with conventional additive manufacturing processes such as selective laser melting or direct metal deposition. Titanium is regarded as a high-performance engineering material due to its unique combination of properties, including good corrosion resistance, biocompatibility and high strength at comparatively low density. However, due to its high price, it appears reasonable for many applications to use material compounds in which titanium is only used on the surface of the workpiece, while less expensive materials such as aluminum are used for the remaining volume. In the present work, cold sprayed pure titanium coatings were deposited on Al substrates and then formed to defined 3-dimensional final contours by die forging and rotary swaging. Different porosities were selectively set in order to evaluate their influence on the coating adhesion and cohesion in the forming process. Pre-consolidation of the coatings and the use of Al/Ti interlayers proved to be promising strategies.

Additive manufacturing processes have been used to produce or repair components in different industry sectors like aerospace, automotive, and biomedical. In these processes, a part can be built by either melted particles as in selective laser melting (SLM) or solid-state particles as in the cold spray process. The cold spray has gained significant attention due to its potential for high deposition rate and nearly zero oxidation. However, the main concern associated with using the cold spray is the level of porosity in as-fabricated samples, altering their mechanical properties. These pores are primarily found in the regions where adiabatic shear instability does not occur. It is worth noting that the deformation of the impacted solid particle plays a vital role in reaching the shear instability. Therefore, for investigating the adiabatic shear instability region, an elastic-plastic simulation approach has been used. For this purpose, it is assumed that an elevated temperature solid Ti6Al4V particle impacts on a stainless-steel substrate surface at high velocity. The results show that increasing particle temperature will significantly enhance particle deformation because of thermal softening. Additionally, they illustrate that a material jet responsible for producing a bonding between particle and substrate by ejecting the broken oxide layer will be formed when the particle has a temperature above 1073 K and substrate remains at room temperature. In the end, it should be noted that increasing particle temperature up to 723 K will not have a significant effect on substrate deformation and final substrate temperature.

Cermets are composite materials consisting of a ceramic reinforcement and a metal matrix. Conventional tungsten carbide cermet parts containing a cobalt matrix phase are mainly produced by powder sintering. Laser Powder Bed Fusion (L-PBF) is an additive manufacturing technology widely applied for direct fabrication of metal functional parts with complex geometry. The present paper deals with the feasibility study of additive manufacturing of cermet parts by L-PBF using WC-17Co powder. The results showed that parametric optimisation of the L-PBF process allowed the production of solid WC-17Co part. Structural analysis revealed the presence of significant porosity (1.41%) and small-scale cracks in the as-built samples. Post-processing, such as HIP (Hot Isostatic Pressure) significantly improved the structure of manufactured parts. The porosity after HIP was very low (0.01%) and phase analysis revealed that the samples after HIP did not contain the fragile W 2 C phase. Abrasive wear tests showed that the wear resistance performance of additively manufactured parts was comparable to a reference produced by powder sintering. High values of hardness (around 1100 HV 30 ) were observed for the as-built and HIP samples. The study successfully demonstrated the possibility of manufacturing wear-resistant cermet parts by L-PBF.

Direct Metal Laser Sintering (DMLS) technique is one of the technologies which is generally used to built prototypes and tooling applications. DMLS uses powder bed fusion to bond particles together by laser energy. A new powder layer is spread on top of the previous layers and the process is repeated up to required shape of part can be produced. This review paper presents development, current status and challenges of the DMLS technique with emphasises on material processed by DMLS and is aimed to understand influence of density, microstructure, micro-hardness, tensile strength and wear behaviour of built-up parts. It also highlights the process through proofs based on classical results in terms of advantages and applications.

In recent years, laser-based post-processing of thermally sprayed coatings has gained significant attention as an alternative post-processing route; to mitigate the microstructural defects such as pores, microcracks, and splat boundaries associated with thermally sprayed coatings. Optimisation of the parameters for the laser post-processing is of paramount importance to maintain the required properties of these coatings. The current thermo-mechanical model simulates the impact of laser heat treatment on thermally sprayed Tungsten Carbide Cobalt (WC-17Co) coating and AISI 316L as substrate. A sequentially coupled transient thermal and structural analysis is performed. Transient temperature field from thermal analysis due to laser source will become input loads for the subsequent stress-strain analysis with appropriate boundary conditions. Both the coating and substrate are given temperature-dependent material properties. A gaussian heat flux distribution is used to model the laser source. The finite element analysis results underline the importance of temperature gradients and the presence of thermally induced stress-strain fields responsible for promoting coating degradation. The obtained results also revealed that heat input and dimensional characteristics play a vital role in the annealing treatment's efficacy. Three separate test cases were considered wherein the hatch spacing was varied, keeping the other parameters (scan speed, laser power, and laser spot diameter) constant. The impact of hatch spacing on the temperature and residual stress distribution across the coating was assessed by this simulation. Residual compressive stress was observed in the coating for two out of the three test cases, which further improved the durability of the coating.

This paper discusses the challenges of constructing mathematical models of physicochemical and heat-mass transfer processes associated with reactive heterogeneous materials used in laser additive manufacturing. The results of calculations of thermocapillary convection induced by laser heating in an aluminum melt with an admixture of nickel particles are presented. Models of interphase and chemical interactions with the formation of intermediate phases and intermetallic compounds on nickel particles added to the melt during laser alloying or cladding are proposed, which make it possible to calculate the composition of intermetallic phases in the trace of the beam after crystallization and cooling.

Tailoring strength and ductility in additive manufacturing or repair is key to successful applications. Therefore, cold spraying must be tuned for maximum amounts of well-bonded internal interfaces as well as sufficient softening of the highly workhardened deposit. Zinc (Zn) with its low melting temperature is an ideal model system to study phenomena associated with high strain rate deformation and local temperature distributions, both, in single impacts and thicker deposits. Bonding and recrystallization can be facilitated by covering selected wide parameter regimes in cold spraying. Despite the low temperatures, Zn single splats already show recrystallization at internal interfaces, the respective amounts then scaling with increasing process gas temperatures. At higher process temperatures, deposits are almost fully recrystallized. The recrystallization seems to improve bonding at internal and at deposit-substrate interfaces. Under optimum conditions, an ultimate deposit cohesive strength of up to 135 MPa and an elongation to failure of 18.4% are reached, comparable to that of laser-manufactured or bulk Zn parts. This demonstrates a welltuned interplay between high amounts of bonded interfaces and softening by recrystallization that allows for deriving bulk-like performance of cold sprayed material without additional posttreatments. Correlations between microstructures, mechanical properties, and fracture mechanisms supply information about prerequisites needed for reaching high ductility as obtained in damage and failure modes of deposits and bulk materials in global and local approaches.

The potential of additive manufacturing has reached a point where the techniques are considered highly relevant for production purposes. In general, the manufacturing industry greets the new approach with enthusiasm, as it offers innovative designs and potentially reduced production costs. However, questions arise concerning the durability of additively manufactured components. This paper describes industrial trials with laser cladding and precipitation hardening heat treatment of thin-walled structures with the 17-4 PH stainless steel alloy. Due to the great relevance of the AM production methods for the aviation industry, the mechanical strength of the alloy given by the MMPDS document is used as a baseline. In order to improve the properties of the produced specimens, hot isostatic pressing was applied. The results show that a post processing treatment consisting of a HIP cycle and a conventional precipitation hardening, vastly improves the mechanical strength and elongation values of printed specimens, causing them to exceed the specified values.

In this study, the effect of laser heat treatment on the deposition of oxide ceramic coatings has been examined preliminary. As the energy source, a fiber-laser irradiation experiment on the fine particle ceramic spray has been examined. This trial will give a new possibility to survey a new type of hybrid aerosol deposition, laser-assisted HAD.

Cobalt chromium (CoCr), a well-known biocompatible material, was additively manufactured using direct energy deposition (DED) technology in this study. Since DED is a relatively new addition to additive manufacturing (AM) processes, there is not enough information about important properties of fabricated parts and components using this technology. This study investigates some important mechanical characteristics of the additively manufactured CoCr using a variety of numerical simulation methods in addition to mechanical tests and experiments. Mechanical experiments such as hardness, wear, and flexural bending test were conducted on DED processed samples. All experiments were also conducted on conventionally processed CoCr specimens for comparison purposes. This study attempts to explain mechanical properties in terms of microstructural characteristics of each sample. DED processed CoCr samples exhibited a complex microstructure with a variety of features such as cellular, columnar, and equiaxed grains within their melt pools. While the DED processed sample had a lower hardness compared to the conventionally processed one, it exhibited a higher wear resistance. These results were discussed in terms of microstructural characteristics and metallurgical bonding knowing that porosity level was negligible in both samples. The out-of-plane mechanical strength of CoCr samples was measured by conducting flexural bending test, and the conventional sample showed a higher flexural modulus than the DED sample. The bend tests were also numerically simulated using two different finite element analysis (FEA) procedures. The FEA results for the DED and conventionally processed samples follow the same trend as the results obtained from the experimental flexural bending test. The layer structure and interfacial bonding of the DED sample could have contributed to the lower flexural modulus compared to the conventional sample.

This paper aims to relate the most important mechanical and fracture properties of Inconel 718 built by the 3DMD technology to the two process parameters directly influencing the thermal gradient, the scanning velocity, and the laser power. To gain a phenomenological understanding of the underlying mechanisms, a complex EBSD study of the obtained materials was performed.