Ni Matrix Research Articles

Electron work function guided tailoring of (W4-x, Mx)C4 /doped Ni matrix interfacial bonding: Insights from first-principles calculations

Heavy tungsten carbide (WC) may cause inhomogeneous distributions in WC-metal matrix composite hardfacing overlays, thus negatively affecting its performance as reinforcement. WC can be lightened by partially substituting W with lighter metals, e.g., Mo and Cr, while maintaining its strength. However, the bonding between modified WC and matrix metals such as nickel (a typical metal-matrix for overlays) is uncertain. This article reports a study on the interfacial bonding between (W4-x, Mx)C4 (M=Mo or Cr) and Ni matrix via first-principle calculations. Different atomic interactions i.e., metal-metal and metal-carbon interactions, at the interface were studied to understand the interfacial bonding through analyses of electron work function (EWF), electron localization function, electronic density of states, bond order, and net charge. It was demonstrated that the lighter (W4-x, Mx)C4 carbides exhibit strong bonding with Ni, comparable to or even stronger than that of WC/Ni interface, and the interfacial bonding includes covalent, ionic and metallic bond components. It is demonstrated that the interfacial bonding can be tuned by doping elements in the Ni matrix with different EWFs, e.g., Mn, Cu, Au, Pt, and Se. Efforts have been made to verify a hypothesis that EWF is an indicator, which can be used to guide selecting effective dopants for tailoring the interfacial bond strength.

The influence of CeO2 on the oxidation resistance of TaC/Ni composites

The in-situ TaC/Ni composites with different CeO2 content (0 wt%, 1 wt%, 2 wt%) were prepared by reactive sintering method, and their oxidation behavior in air at 1073 K was analyzed by static cyclic oxidation method to investigate the influence mechanism of CeO2 on the oxidation resistance of composites. The results show that the CeO2 particles are distributed around the TaC particles in the Ni matrix, and the oxidation behavior of composites with different CeO2 content conforms to the linear kinetic law. The oxide film is mainly composed of NiTa2O6 and a small amount of NiO. The generation reactions of Ta2O5 and NiTa2O6 induce a high expansion and compressive stress in oxide scale, leading to the formation of nonprotective oxide film with pores and cracks on the surface. As the addition of CeO2 increases from 0 wt% to 2 wt%, the thickness of oxide scale on composites obviously reduces from 505 μm to 122 μm, and the Ni and Ta oxides content decreases, leading to the reduction of pores and cracks in oxide scale. The Ce ion generated from the dissolution of CeO2 particles mainly distributes in the Ta oxides during the oxidation process, which hinders the outward diffusion of Ni and Ta ions, resulted in the improved oxidation resistance of TaC/Ni composites.

(Ti,W)C Morphology prediction & (Ti,W)C/Ni Interface bonding characteristics analysis based on first principles and experimental verification

Abstract In order to ensure the feasibility of preparing (Ti,W)C composite ceramic reinforced Ni-based coating by laser cladding, the first principle was used to caculate the electronic structure of (Ti,W)C and predict its morphology. The interface bonding properties of (Ti,W)C/Ni were analyzed through interface construction, and the temperature conditions for in situ formation of (Ti,W)C composite ceramics were obtained through thermodynamic analysis. The in situ preparation of (Ti,W)C/Ni composite coatings was conducted through cladding experiment. The microstructure of the coating was detected by SEM, and the crystal morphology and element composition were analyzed to verify the accuracy of (Ti,W)C morphology prediction. The microhardness of the coating was measured by Vickers hardness tester. The results show that (Ti,W)C composite ceramics can be prepared in situ by laser cladding, and its morphology is hexagon-like. The interface of (Ti,W)C and Ni matrix is well combined, and there are no obvious porosity, cracks and other defects. The (Ti,W)C grains in the coating are fine and uniform.

Electrochemical exfoliation of graphene nanosheets and development of a novel efficient Ni-CeO2-Gr ternary nanocomposite coatings for dual functional anti-corrosion and wear-resistance

Nickel-based coatings offer excellent corrosion, wear resistance, and mechanical strength, and can be further improved with additives, making them ideal for harsh environments like marine and chemical industries. In the present study, graphene (Gr) nanosheets were synthesized via electrochemical exfoliation and a novel Ni-CeO2-Gr nanocomposite coating was prepared by an electrochemical co-electrodeposition technique on a Cu substrate in a traditional Watts bath. The coatings (pure Ni, Ni-Gr, Ni-CeO2 and the ternary Ni-CeO2-Gr) were characterized using optical microscopy, scanning electron microscopy (SEM) coupled with energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), Raman spectroscopy, Vickers microhardness and micro-scratch tests. The electrochemical properties of the coatings were evaluated by electrochemical impedance (EIS) and DC-polarization measurements in 0.5 M NaCl. SEM-EDS, Raman, and XRD analysis confirmed the successful synthesis of high-quality graphene and the incorporation of CeO2 nanoparticles and graphene nanosheets into the nickel coating matrix. It was found that the ternary Ni-CeO2-Gr coating exhibited a high microhardness (915.6 HV), improved cohesive strength and enhanced corrosion resistance (544 KΩ.cm−2) compared to pure Ni coatings (30 KΩ.cm−2) due to the synergistic effect of the graphene and CeO2 duplex layer within the Ni matrix, forming a robust anticorrosion barrier. These findings offer valuable insights into the designing highly efficient materials for corrosion protection.

Preparation of electroless deposition of NiTiZr(P) quaternary alloy and their properties

The exceptional super elasticity and corrosion-resistance of Ni-Ti alloys have attracted a lot of attention and interest lately for a wide range of applications, and complex alloy components could be prepared effectively by different preparation techniques. Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti -Zr(P) binary, ternary, and quaternary alloys were coated on mild steel by electroless deposition which is a method of plating metallic films on a substrate by the reduction of metallic complex ions in solution with the aid of reducing agent from an alkaline bath. The ternary Ni-Ti-Zr(P) alloy is considered to be one of the most promising high-temperature SMAs. SEM, XRD and EDS were used to examine the morphology, phase composition and elemental composition which demonstrate the microstructure of the deposits. The mechanical characteristics of the samples were examined through scratch test and micro hardness analysis and the value increased from 261 HV200 to 405 HV200 and that the coefficient of friction raised significantly from 0.23 to 3.5 owing to the presences of added elements in Ni(P) matrix. Polarization analysis and EIS were tested to evaluate the corrosion properties of coated samples in a non-deaerated 3.5 %wt. (NaCl) solution. The outcomes indicate that as the amount of Ti-Zr elements in the bath raised, the corrosion potential became more positive and the corrosion current density decreased to 14.903 μA/cm2. Furthermore, Ni-Ti-Zr(P) alloy coating strengthens corrosion resistance in comparison to Ni(P).

Influence of SiO2 Nanoparticles Extracted from Biomass on the Properties of Electrodeposited Ni Matrix Composite Films on Si(100) Substrate.

Lab-made biosilica (SiO2) nanoparticles were obtained from waste biomass (rice husks) and used as eco-friendly fillers in the production of nickel matrix composite films via the co-electrodeposition technique. The produced biosilica nanoparticles were characterized using XRD, FTIR, and FE-SEM/EDS. Amorphous nano-sized biosilica particles with a high SiO2 content were obtained. Various current regimes of electrodeposition, such as direct current (DC), pulsating current (PC), and reversing current (RC) regimes, were applied for the fabrication of Ni and Ni/SiO2 films from a sulfamate electrolyte. Ni films electrodeposited with or without 1.0 wt.% biosilica nanoparticles in the electrolyte were characterized using FE-SEM/EDS (morphology/elemental analyses, roundness), AFM (roughness), Vickers microindentation (microhardness), and sheet resistance. Due to the incorporation of SiO2 nanoparticles, the Ni/SiO2 films were coarser than those obtained from the pure sulfamate electrolyte. The addition of SiO2 to the sulfamate electrolyte also caused an increase in the roughness and electrical conductivity of the Ni films. The surface roughness values of the Ni/SiO2 films were approximately 44.0%, 48.8%, and 68.3% larger than those obtained for the pure Ni films produced using the DC, PC, and RC regimes, respectively. The microhardness of the Ni and Ni/SiO2 films was assessed using the Chen-Gao (C-G) composite hardness model, and it was shown that the obtained Ni/SiO2 films had a higher hardness than the pure Ni films. Depending on the applied electrodeposition regime, the hardness of the Ni films increased from 29.1% for the Ni/SiO2 films obtained using the PC regime to 95.5% for those obtained using the RC regime, reaching the maximal value of 6.880 GPa for the Ni/SiO2 films produced using the RC regime.

Effects of helium and vacancy in Ni symmetric tilt grain boundaries by first-principles

The vacancy and helium effects on eight low-Σ symmetric tilt grain boundaries (STGBs) of Ni were investigated by first-principles calculations. The simulations demonstrate that vacancies in Ni matrix could diffuse easily to the grain boundary and helium atoms are quite stable at the grain boundary vacancy sites. Vacancy accumulation at high-energy STGBs could enhance the binding strength while He defects are generally detrimental to grain boundary binding and interstitial helium defects can initiate more severe grain boundary cracking comparing to vacancy-bind-helium. Further electron charge analysis suggested the influence of grain boundary binding greatly relies on the grain boundary atomic structure and the interaction between Ni-d and He-p states. The polarized charge transfer induced by He helium occupation was predicted to be detrimental to the binding strength, which explains the experimentally-observed helium bubbles and helium-induced GB embrittlement.

Ti3AlC2 preceramic paper derived in-situ laminated TiC/Ni-Ni3(Al,Ti) composite: Microstructure, mechanical properties and fracture behavior

In the present study, a biomimetic strategy concerning to surmount the predicament of strength-toughness tradeoff in the Ni matrix composite was carried out. By assembling Ti3AlC2-based preceramic papers with pure Ni foils alternatively, a novel kind of in-situ TiC/Ni-Ni3(Al,Ti) composite with a mimicking nacre architecture was successfully fabricated. The results show that the grain gradient of in-situ TiC combined with γ'-Ni3(Al,Ti) was generated in the composite layer and alloy layer, respectively. The interlayer interface was well-bonded without microvoids, flaws, or other defects. Ascribed to an excellent combination of hard-soft laminate architecture, grain gradient as well as superior interfacial bonding, a synergy of mechanical strength and toughness in the laminated TiC/Ni-Ni3(Al,Ti) composites was achieved. The Vickers hardness increases gradually along alloy layer, interface, and composite layer. The flexural strength and fracture toughness were ∼18 % and ∼92 % higher than the counterpart of homogeneous TiC/Ni-Ni3(Al,Ti) composite. The laminated architecture enhances the efficiencies of gradient TiC grains in mechanical strengthening for required bearing and loading transmission, and toughens composite materials by interfacial delamination, cracks deflection, bridging and blunting.

Creation of a nickel composite using surface structuring of the reinforcing phase with titanium carbide nanostructures to improve strength properties

Abstract The development of metal matrix composite (MMC) materials is one of the demanded areas of research in materials science. In line with this trend, there is an increasing interest in nickel-based MMC materials, which have already become classic in science and technology. This is due to the high demand for Ni-based materials with high strength characteristics, high hardness, and increased heat resistance. In this research, we proposed an approach to obtain a MMC material using the surface structuring process, ALD (Atomic Layer Deposition) and powder metallurgy method. The developed approach provides a composite with TiC nanostructures (1-5 nm) uniformly distributed throughout the Ni matrix. The absence of interphase boundaries between the Ni matrix particles and carbide nanostructures made it possible to minimize the internal porosity of the sample. This is due to the strength of the interphase boundaries between the matrix and the reinforcing phase in the composite and to the solidity of the structure. As a result, the created material effectively resists plastic deformation and stress. This allows not only to enhance the strength properties of the composite, but also to maintain the MMC plasticity, which increases its processing ability.

Influence of pulse frequency on microstructure, mechanical properties, and corrosion resistance of electrodeposited Ni-SiC composite coatings

The current study explores the effects of SiC co-deposition in Ni matrix during pulse electrodeposition (PED) at various pulse frequencies. X-Ray Diffraction (XRD) analysis indicates that at lower frequencies, the composite coating favours the (111) plane orientation, while at higher frequencies (50 and 100 Hz), it changes toward the (200) plane. Scanning Electron Microscopy (SEM) analysis shows a decrease in SiC particle content with increasing frequency. Coatings deposited at 10 Hz display a compact, uniform structure with higher SiC particle concentration, resulting in smoother surfaces compared to pure Ni coatings. This leads to higher hardness (440 HVN) compared to coatings deposited at higher frequencies (425 HVN and 410 HVN for the 50 Hz and 100 Hz, respectively). Furthermore, the composite coatings exhibit superior corrosion resistance, with reduced electrolyte penetration and localized corrosion relative to pure Ni. Notably, the 10 Hz coating demonstrates a lower corrosion rate of 0.005 mm/year and a higher corrosion protection efficiency of 88 %. Therefore, SiC co-deposition at 10 Hz acts as a protective barrier, inhibiting corrosion progression and enhancing long-term durability against corrosion.

Synchrotron X-ray diffraction studies of the internal load transfer in Ni–CrC metal matrix composites

Strengthening in metal matrix composites (MMCs) is primarily due to the load transfer from the compliant matrix to the stiff reinforcement. While internal load transfer has been studied for conventionally manufactured MMCs, the extent to which it may be affected by the preexisting defects in additively manufactured MMCs remain elusive. In this study, we performed uniaxial compression loading on cold sprayed Ni–CrC particulate-reinforced MMC. We observe significantly enhanced strength and ductility compared to the brittle behavior previously reported in tension for the same MMC. In contrast to the absence of load transfer in tension, the presence of initial defects did not preclude the internal load transfer in the composites under compressive loading. In-situ high-energy X-ray diffraction analysis revealed a relatively constant load partitioning in the elastic regime, which aligned well with predictions by the Eshelby's inclusion model. Furthermore, an internal load transfer was observed from the Ni matrix to the CrC reinforcement upon plastic deformation of the Ni matrix. Finite element modeling further confirmed this and demonstrated that localized tensile stress at the interface in the transverse direction resulted in the interfacial debonding and partial relaxation of the matrix. We also report reinforcing particle fracture upon further compression which in turn triggered the eventual failure of the MMC.

Microstructure and Properties of Ni-WC Composite Plasma Clad

aims: This study aims to improve the surface properties of 45 steel to broaden its applications. background: 45 Steel is an important material for the development of human society and civilisation,and plays an important role in human production and life. Ni-based composite coatings are widely used in metal workpieces to improve the surface properties and expand its applications. objective: In this study, Ni-WC composite coating was prepared on 45 steel substrates by plasma cladding. The microstructure, microhardness, residual stress, and corrosion resistance properties were analyzed to examine various influencing factors. method: In this study, the plasma cladding technique was employed to produce Ni-based cladding with different WC contents on 45 steel surfaces. The microstructure, phase structure, microhardness, residual stress, and corrosion resistance of Ni-based cladding coatings were investigated. result: The results showed that the coatings are made up mostly of Ni3Fe, Cr23C6, Cr7C3, WC, and W2C phases. conclusion: The microhardness of the Ni-based alloy coatings is greatly increased due to the presence of WC hard phase on the Ni matrix. The highest microhardness is more than tripling that of the substrate with the addition of 60% WC. In addition, the largest residual stress at the center of the cladding channel is more than five times higher than the substrate affected zone. The corrosion resistance of 45 steels containing Ni-based coatings increases in acidic, neutral and alkaline environments due to the formation of passivation films. other: none

Influence of Borides on microstructure and mechanical properties of a Ni alloy

Abstract Ni alloys are known to exhibit superior creep strength, chemical stability, and thermal resistance behavior at elevated temperatures. However, they also exhibit inadequate mechanical performance. Hence, the microstructures and, in relation to that, mechanical properties need to be improved. In this study, the effect of reinforcement of TiB2 on microstructural and mechanical properties was evaluated. The Ni matrix is reinforced with TiB2 particles. TiB2–Ni composites were successfully produced by the hot pressing method. Homogenously distributed TiB2 particles were observed in the microstructure using the energy dispersive spectrometry (EDS) mapping technique. The hardness of the reinforced samples was considerably improved by 2.65–8.12 times compared to pure Ni and between the different content of borides. A three-point bending test was performed to examine the mechanical behaviors of the reinforced composites. The bending stress properties of metal matrix composite (MMC) were significantly influenced by TiB2 content both positively and adversely. The optimum chemical content was determined based on bending tests and fractography. As a result, the 15 wt.% TiB2-reinforced sample exhibited superior microstructural (density), hardness, and bending properties compared to pure Ni and other reinforced samples with different ratios.

Effect of yttrium oxide addition on the microstructure and mechanical properties of WC–ni composites fabricated from recycled WC and Ni

ABSTRACT WC-Co composites are widely used in cutting tools but are expensive and harmful due to Co in the composites. Alternatives, such as WC-Ni composites have inferior mechanical properties, as a result, WC-Co composites are used in most cutting tools. This study investigated whether adding yttrium oxide (Y2O3) to WC-Ni composites, fabricated from recycled tungsten carbide (WC) and Ni, improved their mechanical properties. Changes in the composites’ microstructure and mechanical properties depended on the amount of Y2O3 added. Y2O3 reacted with WC during sintering, promoting the formation of W and reducing the proportion of C in the composite. The added Y2O3 accelerated the dissolution of W in the Ni matrix, and increased the fractions of the eta phase and solid solution phase. Ni is strengthened by the dissolution of W in Ni, thereby supplementing the low toughness of the eta phase and ultimately yielding WC – Ni with improved hardness and fracture toughness (HV: max. 15.4 GPa, KIC: max. 13.4 MPa∙m1/2) compared to WC – Ni without Y2O3 (HV: 13.5 GPa, KIC: 12.7 MPa∙m1/2). The method for improving the properties of WC – Ni composites by the addition of Y2O3 has a high possibility of commercialization because it does not necessitate process changes.

Direct observation and characterization of a novel long period stacking ordered phase in GH4169 alloy

As is widely recognized, the Long Period Stacking Ordered (LPSO) phase is an important strengthening phase in the rare earth magnesium alloys. The LPSO phase not only enhances the strength of the alloy, but also improves its plasticity, thereby effectively addressing the strength-ductility trade-off phenomenon. Therefore, the preparation of metallic materials containing LPSO phase provides a new idea for designing a new generation of high-strength and high-toughness alloys. In present study, A novel nano-sized LPSO phase is observed and characterized for the first time in GH4169 nickel-based alloy. The results show that the stacking sequence of the LPSO phase is ABCBCBA, which indicates that this LPSO phase has a 6H structure. Meanwhile, the orientation relationships between LPSO phase and the Ni matrix are (11–1)γ//(0006)LPSO and [011]γ//[2-1-10]LPSO.

Inhibition of intermetallic compounds using pure Ni or Ni–Al2O3 nanocomposite coating during the ultrasonic-assisted soldering of Mg/Al dissimilar metals

The widespread utilization of lightweight Mg and Al alloys underscores the importance of establishing reliable connections between them. However, joining dissimilar Mg/Al alloys presents challenges, primarily due to uncontrolled formation of intermetallic compounds during the process, leading to weakened joint performance. To inhibit its formation, a Ni or Ni–Al2O3 nanocomposite coating served as a barrier layer during ultrasonic-assisted soldering AZ31 Mg/6061 Al using Sn–3.0Ag–0.5Cu solder. By investigating the impacts of Ni/Ni–Al2O3 composite coating on microstructure, intermetallic compounds formation, and joint performance, we found that the Ni coating partially inhibited Mg diffusion into the solder at 260 °C for 20 min, thus limiting excessive Mg2Sn compound formation and increasing shear strength by approximately 110% compared to uncoated joints. However, with an extension of the holding time to 30 min, block-shaped Mg2Sn compound reemerged as the primary cause of joint failure. Using Ni–Al2O3 composite coating further broadened the process window of Mg/Al soldering, eliminating block-shaped Mg2Sn compound in the joint at 260 °C for 40 min. The incorporation of Al2O3 further enhanced joint properties, with the maximum shear strength of the Mg(Ni–Al2O3)/SAC/Al joint reaching approximately 66.6 MPa, an improvement of 18.3% compared to the joint with Ni coating. This enhancement shifted the fracture position from the Ni/SAC interface to the SAC solder. Additionally, due to grain refinement in the Ni matrix, the microhardness of the Ni–Al2O3 composite coating surpassed that of the Ni coating. A model of Ni/Ni–Al2O3 composite coating preventing intermetallic compounds formation of was proposed. This nanocomposite coating-ultrasonic assisted soldering method effectively avoids the issue of excessive intermetallic compounds formation when joining dissimilar metals.

Understanding Kirkendall effect in Ni(W) diffusion-induced recrystallization region

This study elucidates the formation of distinct phases, such as intermetallic compounds (IMCs), and the evolution of Kirkendall voids. We not only observed the emergence of polycrystalline IMC layers and distinct diffusion-induced recrystallization (DIR) regions using various experimental methods but also quantified the elusive Kirkendall vacancy fraction by an extended numerical model. Experiments revealed the formation of polycrystalline layers with Ni4W and a distinct DIR region. Irregularly shaped Kirkendall voids were found in the DIR region in the Ni matrix. The observed DIR region thickness exceeding W penetration depth indicated rapid alloying. Experimental data and insights from the Ni-W phase diagram showed exclusive Ni4W formation. EBSD analysis revealed smaller Ni4W grains and larger, irregularly shaped DIR region grains. Quantification of Kirkendall voids through Blob analysis linked numerical results to experiments. Noteworthy findings include the fraction of Kirkendall vacancy and the evolution of the possible vacancy region calculations, highlighting their dependence on the W diffusivity and grain boundary diffusion. Temporal evolution of the vacancy region showed the absence of vacancies near Ni4W/DIR, with the leading edge at DIR/Ni, providing insights into annealing-induced vacancy distribution. This integrated approach enhances understanding of thermodynamics and kinetics in the Ni-W diffusion couple, advancing knowledge crucial for high-temperature materials science applications.

Electrochemical Deposition and Properties of Ni Coatings with Nitrogen-Modified Graphene Oxide

In this study, a method for producing nitrogen-modified graphene oxide (NMGO) using hydrothermal synthesis in the presence of triethanolamine is presented. The composition and structure of NMGO are characterized using X-ray phase analysis (XPA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and Raman spectroscopy. Ni-based metal matrix coatings (MMCs) modified with NMGO were obtained from a sulfate-chloride electrolyte in the galvanostatic mode. The process of electrochemical deposition of these coatings was studied using chronovoltammetry. The microstructure of Ni–NMGO MMCs was studied using the XPA and SEM methods. It has been established that the addition of NMGO particles into the Ni matrix results in an increase in the microhardness of the resulting coatings by an average of 1.30 times. This effect is a consequence of the refinement of crystallites and high mechanical properties of NMGO phase. The corrosion-electrochemical behavior of studied electrochemical deposits in 0.5 M sulfuric acid was analyzed. It has been shown that the corrosion rate of Ni–NMGO MMCs in a 3.5% sodium chloride environment decreases by approximately 1.50–1.70 times as compared to unmodified Ni coatings. This is due to NMGO particles that act as a barrier preventing the propagation of the corrosion and form corrosive galvanic microelements with Ni, promoting anodic polarization.

One‐Pot Synthesis of Carbon‐Supported Pd Nanoparticles with Ni and Carbon Matrix Protection for Durable Alkaline Hydrogen Oxidation Reaction

Protecting nanoparticles with a carbon matrix can enhance the durability of the catalysts in alkaline fuel cells (AFC) and is well‐documented. While others have tried complex syntheses to produce small nanoparticle catalysts, in this work, in order to scale‐up batches of 15 g or more, carbon‐cap (or carbon‐coating) protected Vulcan XC72‐supported Pd‐Ni (1‐2) nanoparticles (Pd‐Niacc/C) were successfully synthesized via a one‐step dry‐synthesis process. This catalyst was compared with a commercial Pd‐Ni/Vulcan XC72 material (PdNi/C, Premetek) in terms of hydrogen oxidation reaction (HOR) activity and stability. To produce less ordered carbon caps (versus graphite/graphene), a low‐temperature heat‐treatment (below 500°C) was used, resulting in Pd‐Niacc/C of unique electrochemical properties: easily electrochemically activated, this catalyst outperforms PdNi/C for alkaline HOR and proves more durable under highly oxidizing accelerated stress test (AST) conditions. Identical location transmission electron microscopy (ILTEM), X‐ray photoelectron spectroscopy (XPS) and rotating disk electrode (RDE) measurements demonstrate how the Ni‐rich surface plays an important role in HOR activity for both PdNi/C and PdNiacc/C and that the protective carbon‐coating of the latter ensures better durability of performance and better resistance to materials degradation.

Influence of Scanning Strategy and Post-Treatment on Cracks and Mechanical Properties of Selective-Laser-Melted K438 Superalloy

The feasibility of manufacturing high-performance components with complex structures is limited due to cracks in some superalloys fabricated by selective laser melting (SLM). By controlling the main process parameters such as scanning strategy, the adverse effects of cracks can be effectively reduced. In this paper, the effects of two different SLM scanning strategies with island and ‘back-and-forth’ and post-heat treatment on the cracks and mechanical properties of selective-laser-melted (SLMed) K438 alloy were investigated. The results show that the SLM method of the ‘back-and-forth’ scanning strategy had better lap and interlayer rotation angles and a more uniform distribution of laser energy compared with the island scanning strategy. The residual stress accumulation was reduced and crack formation was inhibited under this scanning strategy owing to the cooling and shrinkage process. In addition, the dislocation motion was hindered by the formation of uniformly dispersed MC carbides and γ’ phases during the SLM K438 alloy process, which resulted in the density of the as-built SLMed K438 alloy being up to 99.34%, the hardness up to 9.6 Gpa, and the tensile strength up to 1309 MPa. After post-heat treatment, the fine secondary γ’ phases were precipitated and dispersed uniformly in the Ni matrix, which effectively improved the Young’s modulus and tensile strength of the alloy by dispersing the stress-concentrated area.