Effect of Solid Solution Temperature on Material Properties and Microstructure of Inconel 718/TiC Composites by Selective Laser Melting

Graphene is an ideal reinforcement material for metal matrix composites (MMC) owing to its high strength, high ductility, light weight, as well as good bonding with metal matrix. Additive manufacturing such as selective laser melting (SLM) brings the advantages of low material waste, high flexibility, and short production lead cycle. In this study, graphene nano-platelets (GNPs) reinforced Inconel 718 composites are fabricated by SLM technique and processed under various post heat treatment schemes. It is found that fabrication of GNPs reinforced MMC using SLM technique is a viable approach. The obtained composite possesses dense microstructure and enhanced tensile strength. Post heat treatments at two levels of solution temperature (980 and 1220°C) for 1 hour followed by two-step aging are carried out. The experiment results indicate that addition of GNPs into Inconel 718 matrix results in significant strength improvement. At as-built condition, the ultimate tensile strengths are 997 and 1447 MPa, respectively at 0 and 4.4vol.% GNP content. Moreover, under as-built and solution treated condition, high content of GNPs results in overall higher UTS value and the strengthening effect is most significant at as-built condition. Meanwhile, γ′ and γ″ precipitation hardening is suppressed in the GNPs reinforced composite under aged condition due to the formation of MC carbide and depletion of Nb. Incorporating GNPs in Inconel 718 effectively inhibits the grain growth during post heat treatment.

Additive technologies, in particular selective laser melting (SLM), enable to manufacture the products with complex geo­metries. The SLM technique can help to effectively expand the titanium nickelide scope of application. However, SLM is a complex process – numerous factors significantly affect the characteristics of the resulting alloy. When the SLM technique is used, as the material is subject to laser processing, the content of nickel in the alloy drops due to evaporation, which can lead to changes in the tempe­ratures of martensitic transformations. This impact on the resulting alloy characteristics can be regulated by changing the para­meters of the SLM process. The objective of our research was to develop the processing methods for manufacturing samples from two commercial TiNi alloy powders using the SLM technique and to analyze the factors causing defects in the obtained samples. At the same time, processing methods with low values of volumetric energy density were used to reduce possible evaporation of nickel during printing. The initial powders were examined for the presence of impurities or other factors affecting the quality of the manufactured samples. The processing method A4 that we have developed for powder 1 enables to obtain a defect-free sample with the density of 6.45 g/cm3. It was found that none of the processing methods used enabled to obtain a defect-free sample from powder 2 due to presence of a large amount of oxygen impurities, including in particular Ti4Ni2Oх secondary phase, which leads to embrittlement and destruction of the samples. Therefore, high content of oxygen in the initial powders has a negative impact on the quality of the samples manufactured using the SLM technique.

Objective: To evaluate the fitness of bilateral free-end dentition defect removable partial denture framework fabricated by selective laser melting (SLM) technique with different support angles. Methods: After the control group has been set to eliminate the system error, and according to the standard model of bilateral mandibular posterior teeth loss, eighteen titanium alloy removable partial denture frameworks fabricated by SLM technology were divided into 3 groups with support angles of 0° (horizontal group), 45°(45° group) and 90° (vertical group). Plaster cast with duplicated structure of tissue surface of the removable partial denture (RPD) framework was obtained. A three-dimensional scanner was used to scan original and duplicated plaster casts. The gaps between framework and the model in different parts were analyzed using Geomagic Qualify software to evaluate the fitness of the framework with visual method. Results: The framework fits on the plaster model completely, and its tissue surface fitted on the plaster model well. The deviation between frameworks and plaster casts was calculated as follow: the total deviations of the horizontal, 45°, and vertical group were (0.146±0.017), (0.182±0.015) and (0.185±0.022) mm respectively. The mean deviation of the horizontal group was significantly less than those of the 45° group and the vertical group (P<0.05). Moreover, there was no significant difference in the total deviation between the 45° group and the vertical group. The total deviation of occlusal rest of the horizontal group was significantly less than that of the 45° group (P<0.05). However, no significant difference was detected in the deviation of occlusal rest among the vertical group, the horizontal group, and the 45° group (P>0.05). There was no significant difference in the deviation of occlusal rest among the vertical group, the horizontal group, and the 45° group. The deviation of clasp of the horizontal group was significantly smaller than those of the 45° group and the vertical group (P<0.05). Whereas, there was no significant difference in the deviation of clasp between the 45° group and the 90° group (P>0.05). No significant difference was found in the deviation of lingual bar among the three groups (P>0.05). Conclusions: Among the three kinds of bilateral free-end dentition defect RPD framework fabricated by SLM in different support angles, horizontal printing was proved to reach the minimal deviation, even though the fitness of all three kinds of frameworks can fullfil clinical requirements according to previous studies.

Topology optimisation is an effective approach to design extreme lightweight components. However, most of the resulted optimum lightweight components usually have complex structures which cannot be produced successfully by traditional manufacturing processes. Selective laser melting is one of the additive manufacturing processes. It shows powerful capacity in the manufacturing of metal components with complex structures. Therefore, the combination of topology optimisation and selective laser melting shows a promising prospect for metal components. However, support structures were usually introduced during the selective laser melting manufacturing process, which resulted to some disadvantages, for example, the support structures are generally difficult to remove from the original components because it is difficult to clamping and machining. Therefore, a design method was proposed in this study, named lightweight and support-free design method, the detailed design process and advantages were presented. In the design process, topology optimisation was applied to realise lightweight design, and support-free design process was developed to meet the support-free requirement. Finally, as a case, a cross-beam component was designed using the proposed method, and the final model was produced successfully using selective laser melting process. The case study result verified that the proposed design method is effective to design lightweight and support-free industrial metal components for SLM process.

Inconel 718 (IN718) is a nickel based Ni-Cr-Fe super alloy. It has a unique set of properties such as good workability, corrosion resistance, high temperature strength, favorable weldability and excellent manufacturability. Due to its wide range of applications, IN718 is an alloy of great interest for many industries. Meanwhile, additive manufacturing assisted with laser has caught much interest from researchers and practitioners in the past three decades. In this study, IN718 alloy coupons are manufactured by selective laser melting (SLM) technique. The SLMed IN718 alloys are treated by ultrasonic nanocrystal surface modification (UNSM), and the residual stress distributions underneath the surfaces are measured. It is found that residual stress mostly tensile is induced while building the part by the SLM technique. The tensile stresses can be reduced to almost zero value by post heat treatment. Moreover, the heat treatment helps to homogenize the microstructure, and results in the increase in hardness. More importantly, it is observed that UNSM effectively induces compressive residual stresses in the as-built and heat-treated parts. The residual stresses of compressive nature in as built parts has depth of around 530 μm where as in heat treated parts has a depth of around 530μm.

Cobalt–chromium (Co-Cr) alloys have been widely used as dental-restoration materials for many years. This study sought to investigate whether selective laser melting (SLM) is a more appropriate process than traditional casting (CAST) for fabricating dental Co-Cr alloys. Metallurgical microscopy, X-ray photoelectron spectroscopy (XPS), Vickers hardness and nanoindentation tests, and friction and wear tests were used to evaluate the microstructure, surface compositions, mechanical properties, and wear resistance, respectively. Additionally, the biocompatibilities and cell adhesion of the alloys were evaluated with L-929 fibroblasts via CCK-8 assay, Live/Dead staining, flow cytometric analysis, scanning electron microscopy (SEM) observation and real-time PCR (RT-PCR) assay. The XPS results showed that the two alloys were all mainly comprised of Co, Cr, and O. The hardness in the CAST group equaled 7.15 ± 0.48 GPa, while in the SLM group, it equaled 9.06 ± 0.49 GPa. The friction coefficient of SLM alloys remained at approximately 0.46, but the CAST specimens fluctuated significantly. SLM alloys exhibited shallower wear scars and less wear debris compared with CAST alloys, simultaneously. Additionally, there were higher survival and expression of cell-adhesion-related genes on SLM alloys of L-929 cells, which meant that the deleterious effect on L-929 cells was significantly reduced compared with that for the CAST alloys. Overall, the wear resistances and biocompatibilities of the Co-Cr dental alloys were dramatically affected by the fabrication technique. The SLM technique is advantageous over the CAST technique for fabricating Co-Cr dental alloys.

The effect of repeated baking of porcelain on its bonding strength to a Co-Cr alloy 3D-printed by selective laser melting

Study on the designing rules and processability of porous structure based on selective laser melting (SLM)

Molded interconnect device (MID) technology is a key enabling technology with growing markets in automotive, communications, consumer electronics through integration with lighting and sensor technologies. Additive manufacturing (AM) is also a key technology as energy, material and resource efficient alternative to conventional subtractive and formative production technologies. In this contribution, powder-based additive layered manufacturing mainly selective laser melting (SLM) is focused to check the potential for substrate manufacturing, system integration and packaging concepts in electronic systems particularly for high-temperature MID applications. The challenge for an optimal mechatronic integrated device design is to simultaneously consider both the application-specific requirements and to integrate advantages of MID technology. This work focuses on the process development for the generation of conductive patterns on ceramic substrates by SLM technique. The process influencing parameters such as laser power, velocity and scan concepts were tested to check the bonding characteristics. The obtained layer thicknesses and the corresponding process-generated failure mechanisms and the mechanical stability are presented. The potential of SLM for high temperature applicability is further discussed. The influences of the printed powder height, laser parameters in combination with laser scan strategies and pattern height are discussed. The hurdles and prospects of SLM as alternative for functionalization are highlighted and discussed.

A comparison on metallurgical behaviors of 316L stainless steel by selective laser melting and laser cladding deposition

Effect of manufacturing techniques on the marginal and internal fit of cobalt-chromium implant-supported multiunit frameworks

Comparative clinical evaluation of removable partial denture frameworks fabricated traditionally or with selective laser melting: A randomized controlled trial

Laser assisted additive manufacturing (LAAM) is regarded as a complementary method to traditional manufacturing processes and it has drawn significant attention from both industry and academia. Improving the performance of components fabricated by LAAM has been an important research task in recent years due to the inevitable negative effects introduced by in the LAAM process, such as porosity, inhomogeneity, and tensile residual stress. In this study, to obtain high-performance metal components by LAAM, nano-TiC particles are adopted to reinforce Inconel 718 and the mixed powders of TiC and Inconel 718 are processed by selective laser melting (SLM). To investigate the effect of TiC concentration on the property and performance of the metal matrix composite, samples with three levels of nano-TiC addition (0, 0.25, 0.5 wt.%) are prepared, in which the SLM process parameters are kept the same for all cases. Three-point bending tests are performed to determine the optimum nano TiC addition. It is found that the material of 0.5 wt.% TiC addition results in the highest bending modulus. Compared with pure Inconel 718, the composite with 0.5 wt.% nano-TiC shows 38% increase in flexural modulus. In addition, to better understand the reinforcing mechanism of nano TiC particles, the SLM processed samples are characterized using a self-designed micro/nano three-point bending tester that is incorporated with an atomic force microscope (AFM) to in situ observe the nanoparticles movement on the sample surface under loading. The sample surface is scanned by AFM at 0%, 2%, 4% and 6% strain condition during the test, and the migration of individual nano particles at the sample surface is tracked at each strain condition. The AFM observations show that the dispersion of TiC nanoparticles is overall random and uniform in the Inconel 718 matrix, and localized agglomeration of TiC particles exists. The interfaces between nanoparticles and the matrix are generally continuous and free of any deleterious micro cracks, indicating a favorable metallurgical bonding feature. The surface morphologies obtained by AFM at different strain conditions are processed by digital image correlation technique to obtain the strain fields during the deformation process. The results show that the agglomerated TiC particles serve as defects in the material, leading to relative sliding of particles with respect to the matrix. This is believed to be the main factor that limits the performance of the composites made by SLM.

Metal–ceramic bond strength of Co–Cr alloy fabricated by selective laser melting

Selective laser melting of a stainless steel and hydroxyapatite composite for load-bearing implant development