M23C6 Carbides Research Articles

Improved creep strength of 10% Cr steels with low N and high B content via increasing quenching temperature

An increase in quenching temperature from 1050 °C to 1100 °C is found to be an effective approach to improving the creep strength at 650 °C in two Re-containing 10% Cr martensitic steels with low N and high B contents. Creep time at creep tests of 650 °C/120 MPa increases at the expense of the appearance of the steady-state creep stage in both steels. Moreover, the room yield strength and ultimate tensile strength are also increased by 10% with increasing quenching temperature in the steel with 0.8% Cu, whereas tensile tests at 650 °C do not reveal the increment in strength in both steels. Improvement in creep and tensile properties is caused by an increase in particle strengthening due to M23C6 carbides, mainly in both steels. The NbX, VX, and “Cu”-clusters/precipitates make minor contributions to the change in particle strengthening. Refinement of M23C6 carbides in both steels is accompanied by an increase in particle number density along the martensitic laths and an increase in the fraction of fine particles with sizes below 50 nm. Such changes in M23C6 carbide dispersions are caused by an increase in the lath area per unit volume and the enrichment of the solid solution with boron because of the dissolution of W2B particles with increasing quenching temperatures.

Investigation of high-temperature wear behavior of Ni-Mo alloyed hardfacing coatings applied on hot strip mill vertical rolls by submerged arc welding

In this study, hot strip mill vertical rolls made of AISI 4140 steel, commonly used in the iron and steel industry's hot rolling section, were coated with ER430 and E430+EC410NiMo using the submerged arc welding (SAW) method. The coatings were characterized through scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness, and wear testing (room 24 °C, 300 °C, and 600 °C). XRD analysis showed that in the ER430 sample, the dominant phase was α-ferrite phase and a small amount of γ (austenite) phase observed, while in the ER 430+EC410NiMo sample, the α-ferrite phase was the dominant phase, but the γ (austenite) phase in the structure was more severe and additionally M6C carbide phase was formed. Coating thicknesses and microhardness values of ER430 and ER430+EC410NiMo coatings were measured as 1.5 mm and 3.75 mm thicknesses, and 533±42 HV0.1 and 473±35 HV0.1 respectively. The increase in hardness on the surface of coated specimens resulted in higher wear resistance compared to the uncoated specimens under all conditions. Regarding average friction coefficient values, coated specimens generally exhibited lower values, although in some cases, the average friction coefficient was higher. In the wear tests, the lowest wear volume losses occurred in the tests conducted at 300°C, while the highest wear volume losses were observed in the tests at 600°C. Upon evaluating the wear mechanisms, it was determined that adhesive and oxidative wear mechanisms were generally dominant in the coated specimens. At higher temperatures, oxidative wear mechanisms became more prominent. ER430+EC410NiMo coatings exhibited better wear resistance compared to ER430, which can be attributed to the toughness effect of γ (austenite) and M6C phases in these coatings. Consequently, it was concluded that applying powder deposition coatings onto hot strip mill vertical rolls made of AISI 4140 steel could enhance their wear resistance, thereby increasing productivity in manufacturing processes.

Creep strength breakdown and the change in back stress strengthening in 10 % Cr martensitic steels during creep at 923 K

The creep strength breakdown in 10 % Cr martensitic steels appeared under creep conditions at a temperature of 923 K and the applied stresses below 120 MPa as a declination from linear regression obtained using short-term creep data. To reveal the origin of creep strength breakdown, the back stress strengthening conception was used. In the initial state, both 10 % Cr martensitic steels had a tempered martensite lath structure with a high dislocation density in the lath interiors and in the lath boundaries, which was stabilized by M23C6 carbides, NbX carbonitrides, and M6C carbides. The shear internal back stresses of 57.5–68.5 MPa and 35–37 MPa were obtained from the creep rate – stress relationship for the regions of high applied stress (above 120 MPa) and low applied stress (below 120 MPa), respectively. The transition from the high stress region to the low stress one in both steels was accompanied by a significant decrease in the dislocation density by an order of magnitude as well as a decrease in particle number density and an increase in the inter-particle spacing in the M23C6 carbide and Laves phase particles located at the low-angle boundaries of the martensitic laths/subgrains. The root mean square superposition of the dislocation and particle contributions to the shear internal back stresses gave the best coincidence with the values obtained from the creep data. The stability of the M23C6 carbide and Laves phase particles located at the low-angle boundaries was concluded to be the key factor suppressing the creep strength breakdown in the 10 % Cr martensitic steels.

Understanding the high-temperature deformation behavior of additively manufactured γ'-forming Ni-based alloys by microstructure heterogeneities-integrated creep modelling

Additively manufactured (AM) alloys present unique and heterogeneous microstructures due to the complex, highly dynamic laser-material interactions. These AM-inherent heterogeneities impede the widespread adoption of AM components, necessitating a profound comprehension of their impact on mechanical properties. Despite extensive research on AM of Ni-based alloys, limited attention has been paid to their creep behavior due to the time-intensive nature of creep tests and the long research cycles. Moreover, experiments and conventional alloy-centric approaches to creep modelling are deemed insufficient in quantifying the effects of AM-specific heterogeneities on creep cavity acceleration and in incorporating the microstructural evolution during creep. To address this critical knowledge gap, a novel computational framework was developed within the structure-property paradigm to unravel the intricate mechanisms governing creep properties. A mechanistic creep model was formulated based on fundamental dislocation creep mechanisms, encompassing dislocation climb-glide motion controlled by γ' precipitates, grain-boundary-sliding (GBS) resistance resulting from M23C6 carbides, and the kinetics of cavity formation. The framework integrates the in situ nucleation, precipitation, and coarsening of γ' precipitates during creep by a precipitation model. The results revealed an excellent agreement in terms of γ' precipitate evolution, creep strain, and strain-rate evolution, the predicted creep life, and times to 1 % strain. By elucidating the intricate interplay between microstructural heterogeneities and creep behavior on the cavity nucleation and GBS mechanisms, the developed computational framework provided valuable insights for enhancing the performance of Ni-based alloys manufactured through AM.

Ultrahigh surface hardness and excellent hardness gradient induced by ultrafine dual-carbides in a novel stainless bearing steel

A novel alloy composition design (Fe–14Cr–13Co–5Mo–2Ni–1W–1V-0.16C-0.12Nb-0.074Si-0.027Mn, wt. %) was proposed for modification on that of the conventional CSS-42L stainless steel. The present homogeneous structure without carburizing displays an excellent synergy of yield strength and fracture toughness, which should improve the performance of the corresponding case-carburized steels under the contact/bending fatigue conditions. An ultrahigh surface hardness (71 HRC) and an excellent hardness gradient along the depth are achieved in the present case-carburized gradient structure. Higher surface hardness at a temperature range of 200–400 °C is also observed in the present case-carburized gradient structure, as compared to the other case-carburized advanced bearing/gear steels, such as the M50 steel, the M50NiL steel and the conventional CSS-42L steel. Besides the previously reported M6C carbides in the case-carburized conventional CSS-42L steel, M7C3 carbides are newly discovered in the present case-carburized gradient structure due to the novel chemical design. The ultrahigh surface hardness at both room and high temperatures and the excellent hardness gradient distribution in the present case-carburized gradient structure should be attributed to the increased amount of dual-carbides, as well as the ultrafine dual-carbides embedded in the ultrafine martensite matrix. The superior mechanical properties of the present case-carburized gradient structure should be desirable for real bearing/gear applications.

New insights into the stress rupture life enhancement mechanisms of a nickel-based superalloy

In this paper, the effects of hot isostatic pressing (HIP) and heat treatment (HT) on the stress rupture properties of nickel-based superalloy K417G were investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were employed to analyze the microstructure, fracture morphology, determination of crack source and dislocation evolution after stress rupture fracture. The results indicate that, HIP specimens demonstrate a 19.5% reduction in stress rupture life compared to as-cast specimens, whereas HIP + HT specimens exhibit a 41% increase in stress rupture life, reaching a value of 63.04 h. The fracture mechanism of the samples under different heat treatment conditions is different. There are a large number of pores in the as-cast specimen, which leads to the initiation and propagation of cracks and eventually result in fracture. The pores in the HIP specimen are almost eliminated. However, the coarsening and uneven distribution of γ′ phase led to the weakening of the hindrance to dislocation movement. Additionally, the increase in elongated carbides at grain boundaries accelerates crack initiation and propagation. Under HIP and HT, the cubic γ′ phase is uniformly precipitated, which effectively hinders the movement of dislocation lines. Granular M23C6 carbides precipitate at grain boundaries, acting as pinning points to retard grain boundary sliding and crack propagation, thus improving the stress rupture life.

Effect of solid-solution treatment on high-temperature properties and creep fracture mechanism of laser powder bed fused Inconel 625 alloy

Laser powder bed fusion (LPBF) has been widely used for fabricating Inconel 625 (IN625) alloy, and it is widely regarded as a promising manufacturing technology. However, during high-temperature service, the γ″ strengthening phase of LPBFed IN625 gradually transforms into the detrimental δ phase. Controlling the morphology and distribution of precipitates is necessary for optimizing high-temperature performance. This study compared the as-built and 1090 °C solution-treated LPBFed IN625 alloy and investigated the microstructure evolution, tensile properties, and creep fracture behavior at a high temperature of 815 °C. The results show that the solid-solution treatment improves the creep ductility of LPBFed IN625 alloys at 815 °C by forming a high percentage of twinned boundaries and eliminating dislocations. The formation of coarsened needle-like δ phases and carbides during creep reduces the strength of the grain boundaries and is responsible for creep fracture failure. During creep of the as-built samples, the irregular Laves phase between the columnar dendrites gradually transforms into plate-like δ phases and M6C carbides uniformly and densely distributed within the columnar grains. The precipitation-strengthening effect of these fine precipitates, combined with the initial high density of dislocations and strong texturing effect, brings favorable high-temperature strength and creep fracture life but consequently leads to low creep ductility.

Temperature/stress dependence of stress rupture behavior and deformation microstructure of an advanced superalloy for additive manufacturing

A self-developed crack-free advanced superalloy ZGH451 fabricated by direct energy deposition (DED) was applied to investigate the microstructure evolution, stress rupture behavior, and deformation mechanisms at moderate-high temperatures and high-low stress conditions. The high Ta/Al ratio induces large misfit lattice stress and low stacking fault energy of alloy, resulting in approximate cubic γ′ phases in dendrites and the formation of initial dislocation tangles. After the stress rupture test at 760 °C/780 MPa, high content cubic γ′ phases, small size of voids as well as preserved dislocation tangles are observed, showing stable structures with high-stress rupture resistance. High content and suitable size of cubic γ′ phases, initial dislocation tangles, and L-C locks hinder the dislocation motion, which decreases the minimum strain rate and prolongs life significantly, forming four stress rupture stages. Hence, the deformation mechanism is determined by dislocation piled-up on γ/γ′ interface, formation of stacking faults in γ′ phases, and dislocations shearing γ′ phases. However, the microstructure exhibits uneven structures composed of large sizes of rafted γ′ phases and voids at 980 °C/260 MPa. The rafted structure and high temperature provide continuous channels and enough energy for dislocation motion, resulting in the increase of minimum strain rate, decline of life, and typic three stress rupture stages, even though there are obstacles to dislocation movement caused by dislocation networks. The deformation mechanism transforms to form dislocation networks on γ/γ′ interface and dislocations shearing γ′ phases. Besides, the decomposition of carbides on GBs also depends on temperature, which decomposes into harmful chain-like M23C6 carbides at moderate temperatures and reinforced granular-shaped M6C carbides at high temperatures. The applied stress always decreases mechanical properties due to its degradation of microstructure induced by elongating the precipitates and defects.

Corrosion behavior of δ-ferrite in AISI 316 austenitic stainless steel exposed to oxygen-saturated lead‑bismuth eutectic at 550 °C

δ-ferrite is usually found in the 300 series austenitic stainless steels (ASS), but the role of δ-ferrite on corrosion behaviors exposed to oxygen-controlled lead–bismuth eutectic (LBE) has not yet been elucidated. The corrosion behaviors of AISI 316 ASS containing δ-ferrite in the oxygen-saturated static LBE at 550 °C were studied in terms of their solution-treated and accelerated-aging treated conditions. The δ-ferrite and decomposed δ-ferrite exhibit the superior resistance to oxidation attack compared to the austenite, and the δ-ferrite possesses a better corrosion resistance than the decomposed δ-ferrite. Compared with the austenite, the higher diffusivities of Cr and Si in δ-ferrite cause a reduction in the critical concentration required for the formation of chromium oxide and Si-rich oxide. A mixture of Cr2O3 oxide and Fe-Cr-Si spinel oxide developed on the surface of δ-ferrite can effectively impede the metal transfer, leading to the superior resistance to oxidation attack. The retained δ-ferrite and M23C6 carbides in the decomposed δ-ferrite oxidizes independently into FeCr2O4 and Cr2O3 oxides, respectively. The presence of Cr2O3 scale around the retained δ-ferrite decreases its oxidation rate, resulting in the non-uniform oxide phenomenon.

Characteristic analysis of high-speed steel powder prepared by gas atomisation

The performance of high-speed steel (HSS) powder is a prerequisite for the preparation of high-performance powder metallurgy HSS. The physical properties, microstructure, and solidification characteristics of HSS powder prepared by nitrogen gas atomisation were systematically studied and analysed in detail. For the atomised TPM558 HSS powder, the morphology is spherical and the particle size distribution is wide. The smooth small particles of satellite powder attach to the surface of large particles. Shrinkage pits caused by solidification shrinkage exist on the surface of large particles. The average cooling rate is between 104 and 106 K·s−1, with the increase of cooling rate, the powder surface tends to be smooth, and the grain structure is transformed in the order of cellular to dendritic to radial. The single powder particle surface shows fine-equiaxed grains, while the internal presents columnar grains. The crystalline phases of the powder are austenite, ferrite, martensite, and carbide, and the carbide includes MC carbide with face-centred structure and M2C carbide with hexagonal structure. The average nano-hardness of the powder is 9.93 GPa, resulting in poor formability, and it can be pressed and formed only after adding binder.

Austenite decomposition behavior adjacent to δ-ferrite in a Si-modified Fe-Cr-Ni austenitic stainless steel during thermal aging at 550 °C

The δ-ferrite decomposition has been widely reported in conventional Fe-Cr-Ni austenitic stainless steel during thermal aging. However, a novel phenomenon is found in a Si-modified austenitic stainless steel, that δ-ferrite decomposition is suppressed, replaced by the decomposition of adjacent austenite. Herein, the decomposition behavior of austenite adjacent to δ-ferrite and its effect on impact toughness in a Si-modified austenitic stainless steel during aging at 550 °C up to 3000 h have been investigated. During thermal aging, austenite adjacent to δ-ferrite is decomposed in the following sequence: (1) γ → M23C6 + α transformation takes place. The preferential formation of secondary M23C6 carbides not only rejects Si atoms into the surrounding austenite but also produces a C-depleted zone. The transformation of austenite to ferrite is induced in the Si-riched and C-depleted micro-zone. (2) The growth of secondary M23C6 carbides induces a continuous rejection of Ni and Si atoms into M23C6/γ and M23C6/α interfaces, and the strong attractive interaction between Ni and Si provides the chemical driving force for nucleation of M6C carbides and G-phase. (3) With prolonged aging time, the lower C, high Ni, and high Si concentrations in the frontier of decomposed austenite will promote the preferential precipitation of M6C carbides rather than M23C6 carbides. During impact deformation, microcracks caused by strain incompatibility between secondary M23C6 and α-ferrite, resulting in a slight decrease in impact toughness. As austenite decomposition proceeds, the higher strain incompatibility across M6C/α interfaces leads to brittle cleavage fracture, resulting in a significant decrease in impact toughness.

Microstructure and tribological properties of solid lubricant-doped CMT-WAAMed Stellite deposits

AbstractA large share of the world’s total energy consumption is used to overcome friction. Therefore, low friction wear-resistant materials are needed. Solid lubricants are solid-phase materials that can reduce friction at different temperatures between two surfaces sliding against each other without the need for a grease or liquid oil medium. In this study, Cold Metal Transfer Wire Arc Additive Manufacturing (CMT-WAAM) was used to deposit solid lubricant (WS2, MoS2, CaF2) doped hypoeutectic Stellite alloy. Fabricated deposits possessed crack- and pore-free microstructures consisting of γ-Co and M7C3 carbide eutectics embedded with chromium sulfides and microhardness values of ~ 530 HV1. They were also tested in self-mated unidirectional sliding wear tests in dry conditions at room temperature (RT) and at 300 °C in an air atmosphere. The results showed that the dynamic coefficient of friction (COF) decreased ~ 27% at RT and ~ 21% at 300 °C without losing the wear properties. During sliding wear tests severe strain hardening occurred and γ-Co was found to transform to ε-Co. The developed deposits can be used as hard facings or 3D printed components in applications that require good sliding wear properties at different temperatures such as metal forming tools, power transmission components, valves, and internal parts of combustion engines.

Effect of melt temperature on the quasi-equilibrium solidification of K465 Ni-based superalloy

The solidification process of Ni-based superalloy K465 was examined using DTA and X-ray diffraction. The impact of melt structure on solidification process and the morphology of MC carbide and γ′-phase was analyzed. It was observed that an increase in melt peak temperature led to a significant decrease in precipitation temperature for carbides, but only a slight increase in the formation temperature of matrix and eutectic microstructure. The X-ray diffraction results showed that some ordered structures were detected in the sample with melt peak temperature of 1450 °C and 1500 °C, but not in the sample with melt peak temperature of 1360 °C. Furthermore, the ordered structure displayed similar crystalline features with M6C carbide. As the melt peak temperature increased, the carbides changed from block type to script type morphology. This phenomenon was likely caused by the formation of ordered structures at high temperatures. However, the microstructure of γ matrix and γ′ precipitates remained unaffected by the melt peak temperature.

Effect of Ta addition on primary MC carbide in Ti-Nb-Mo-W-alloyed superalloy

The effect of Ta addition on characterization of primary MC carbides with regard to their morphology, composition, and size in Ti-Nb-Mo-W-alloyed Ni-based superalloy were investigated. Several tools including automated scanning electron microscopy as well as electrolytic etching technology were used for broad characterization of carbides including three-dimensional morphology. The addition of Ta significantly influences the composition and morphology of primary MC carbides. Large dendrite (Ti,Nb,W,Mo)C carbides were changed to smaller (Ta,Ti,Nb)C carbides. The hardness of both MC primary carbides and the matrix were increased. MC carbides in the studied superalloys were developed dendrite in three-dimensional morphology, which was much larger than that in two-dimensional morphology. The formation mechanism of carbides was clarified by thermodynamic calculation.

Effect of ageing temperature on the microstructural evolution and mechanical properties in M2C and NiAl co-precipitation secondary hardening ultrahigh-strength steel

A novel cost-effective secondary hardening ultrahigh-strength steel, strengthened by the co-precipitation of M2C and NiAl, was developed. The present study systematically investigated the co-precipitation evolution, austenite reversion, and mechanisms of strengthening and toughening at different ageing temperatures. As the ageing temperature increased, the quenched microstructure underwent various transformations, including precipitation and dissolution of cementite, nucleation and coarsening of M2C and NiAl nanoparticles, as well as reversion of austenite. At ageing temperatures of 427 °C and 454 °C, a small amount of cementite was present in the martensite matrix, and M2C and NiAl precipitates started to form, resulting in low strength and poor toughness. At 482 °C, the peak-ageing stage was reached, achieving a maximum yield strength of 1875 ± 4 MPa and an ultimate tensile strength of 2185 ± 3 MPa. This strength is primarily attributed to shear strengthening of NiAl particles and Orowan strengthening of M2C carbides. Additionally, the complete dissolution of cementite at this stage improved toughness. As the ageing temperature increased to 510 °C and 538 °C, the strength decreased due to coarsening of M2C, while the toughness improved as a result of film austenite reversion and enhanced dislocations bypassing around the M2C carbides.

A Comprehensive Study on Microstructure and Wear Behavior of Nano-WC Reinforced Ni60 Laser Coating on 17-4PH Stainless Steel

The surface of 17-4PH martensitic stainless steel was laser-cladded with Ni60 and Ni60+nano-WC composites and a comprehensive investigation was conducted of the microstructure and wear mechanism. The findings demonstrate that despite the added nano-WC particles being fused and dissolved during laser cladding, they still lead to a reduction in grain size and a decrease in crystallographic orientation strength. Furthermore, the dissolution of nano-WC makes the lamellar M23C6 carbides transform into a rod or block morphology, and leads to the CrB borides becoming finer and more evenly dispersed. This microstructural evolution resulted in a uniform increase in hardness and wear resistance, effectively preventing crack formation. When the nano-WC addition increased to 20 wt.%, there was a 27.12% increase in microhardness and an 85.19% decrease in volume wear rate compared to that of the pure Ni60 coating. Through analysis of the microstructure and topography of wear traces, it can be inferred that as the nano-WC addition increased from 0 wt.% up to 20 wt.%, there was a gradual transition from two-body abrasive wear to three-body abrasive wear, ultimately resulting in adherent wear.

Effects of Oxygen Content on Microstructure and Creep Property of Powder Metallurgy Superalloy

The effects of oxygen content on the microstructure and creep properties of the FGH96 superalloy were investigated. When oxygen content increased from 135 ppm to 341 ppm, the prior particle boundary (PPB) rose from degree 2 to degree 3, the size of the γ′ phase on PPB enlarged from 1.07 μm to 1.27 μm, and the MC carbide size grew from 77.4 nm to 104.0 nm. Meanwhile, the steady creep rate accelerated from 4.34 × 10−3 h−1 to 1.87 × 10−2 h−1, and the creep rupture life shortened from 176 h to 94 h, the creep rupture mode transferred from intergranular and transgranular mixed fracture to along PPB fracture. During creep, the micro-twin formation and gliding will be restrained by ∑3 boundaries. FGH96 superalloy with higher oxygen content contains less ∑3 boundaries, and its micro-twins cross-slipped instead of single-direction slip in lower oxygen content superalloy. Consequently, samples with a higher oxygen content crept faster and ruptured earlier.

The effect of Hafnium on the microstructure and tensile property in a Ni-based superalloy

The effects of Hafnium on the microstructure and tensile property of a Ni-based superalloy after solution heat treatment and long-term thermal exposure were investigated with field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD). The results revealed reveal that Hf intensified intensifies the element segregation and promoted promotes the precipitation of MC carbide and honeycomb-like Ni5Hf phase in the as-cast alloy. The solid solution strengthening and second phase (MC) strengthening effects are both enhanced in the alloy doping 0.5 wt% Hf after solution heat treatment. Therefore, the tensile yield strength at 700 °C of the alloy with 0.5 wt% Hf is higher than that in the Hf-free alloy. Otherwise, a large amount of the low melting point Ni5Hf phases appear in the alloy with 0.8 wt% Hf. Ni5Hf phase is prone to become the crack initiation, which decreases diminishes the yield strength in the alloy with 0.8 wt% Hf. The addition of 0.5 wt% Hf can inhibit the formation of needle-like δ phase at grain boundary due to the decrease of grain boundary energy and diffusion rate at grain boundary. Therefore, the 700 °C tensile strength and ductility increase simultaneously in the alloy with 0.5 wt% Hf after thermal exposure at 700 °C.

Process parameter optimization for laser powder directed energy deposition of Inconel 738LC

Processing nickel-based superalloys is one of the major challenges in the additive manufacturing (AM) field. Nickel-based superalloys consist of several alloying elements, which make them prone to the formation of undesired phases and cracking due to the complex thermodynamics during the metal AM processes. In order to produce defect-free parts from nickel-based superalloys via metal AM processes, optimization of process parameters is required. In this study, the effect of laser powder directed energy deposition (LP-DED) process parameters on the geometrical properties and porosity ratio of Inconel 738 LC (low carbon) is investigated. Geometrical specifications, including the track height, width, and wetting angle are the major factors that indicate the quality of the final product. The analysis of variance (ANOVA) and response surface methodology (RSM) were developed in order to predict the geometrical specifications of single tracks from the key process parameters, namely laser power, scan speed, and powder feed rate. An optimum set of process parameters was obtained through multi-objective optimization by minimizing the porosity ratio, crack formation and maximizing the deposition rate. The results were verified and a good agreement with the experimental measurements was achieved. The produced bulk sample showed less than one percent porosity content, which indicates the effectiveness of single-track optimization prior to bulk sample production. The overall microstructure of the bulk sample showed a high content of MC carbides resulting from the abundance of alloying elements.

Effect of ultrasonic shot peening on microstructure and mechanical properties of GH3230 superalloy during selective laser melt solution heat treatment

Additive manufacturing (AM) is widely used because of its well-known advantages, but there are some disadvantages including microstructure inconsistencies and harmful residual stresses, which can lead to premature part failure. In this study, the microstructure, and mechanical properties of GH3230 alloy processed by AM are changed by a new post-treatment method, which combines thermal solution treatment (ST) and ultrasonic shot peening (USP). The microstructure evolution of GH3230 after ST and USP after ST is investigated experimentally. The experimental results show that equiaxed crystals and M23C6 carbides appear after solution treatment. After ST, USP is performed, and the gradient microstructure is formed perpendicular to the shot peening surface. Dislocation entanglement and grain refinement occur in the plastically deformed layer. In addition, the carbide interacts with the dislocation. After ST, USP can produce a high level of residual compressive stress in the plastic deformation layer. This combination of ST and USP helps to improve the mechanical properties of additive manufactured parts by changing their microstructure and residual stress distribution.