Aging Heat Treatment Research Articles

Investigation Mechanical and Microstructural Behavior of Operated and Unoperated Turbine Rotor Discs

In gas turbine engines, turbine sections are exposed to high temperature and loads during operation and therefore turbine inlet boundary is considered the most challenging for turbomachines. Ni-based super-alloys are used for turbine materials in gas turbine engines because of their superior mechanical characteristics at high temperatures. In this research, two Mar M-247 polycrystalline cast Ni-based turbine rotors, which were operated and non-operated in turbojet engine tests, had the same design and applied the same two-step aging heat treatment, were examined microstructurally and mechanically. As a result of the mechanical analysis, it was observed that the tensile strength (Rm (P): 537Mpa; Rm (G): 590 Mpa) ductility, and hardness (429 HV (P), 440 HV (G)) of the operated turbine rotor increased. In the microstructure analysis, blocky and Chinese script-like carbides and gamma prime eutectic islands were found in both turbine structures. EDS analysis showed that the carbides in the matrix are rich in Hf, Ta, and Ti, and the grain boundary carbides are rich in Cr and W.

Investigation of Mechanical, Corrosion and Microstructural Behaviour of Heat Treated Cr-Modified Al-Mg-Si Alloy

Despite the choice of Al-Mg-Si alloy as a material for innumerable industrial and structural applications, challenges such as undesired scratch resistance, formability and mechanical properties deterioration in saline environment hinders the extent of its application for automotive and aerospace components. Nevertheless, with the growing interest in the application of Al-Mg-Si alloy in automotive and aerospace industries, there is need for cautious control of thermal treatments and inclusion of alloying elements with requisite potentials for enhancing the microstructure and mechanical properties of the alloy. Chromium is known to improve strength and corrosion resistance in several applications. Therefore, this study focuses on the investigation of the effect of Cr particles inclusion in Al-Mg-Si alloy. The effect of ageing heat treatment on selected properties of Al-Mg-Si-Cr alloy was also studied in this work. The Al-Mg-Si and Al-Mg-Si-Cr alloys were developed using a two-step stir casting technique. Chromium was added to Al-Mg-Si alloy at varying percentages of 0, 0.5, 1.0, 1.5, 2.0 and 2.5. All the samples were solution treated in an electric furnace at 500 oC for 30 minutes and water quenched. Then the samples were artificially aged at 210 oC for 3 hours and quenched in natural air. The hardness test revealed that the inclusion of Cr particles in Al-Mg-Si alloy samples increased hardness from 35.03 Kgf/mm2 (hardness of Al-Mg-Si-0%Cr alloy sample) to a maximum value of 126.54 Kgf/mm2 (hardness of Al-Mg-Si-1.5%Cr alloy sample). After heat treatment, the hardness of Al-Mg-Si-0%Cr alloy sample increased to 80.84 Kgf/mm2, while that of Al-Mg-Si-1.5%Cr alloy sample decreased slightly to 120.88 Kgf/mm2. The impact strength test also showed that the inclusion of Cr in Al-Mg-Si alloy increased impact strength from 9.52 J/mm2 (impact strength of Al-Mg-Si-0%Cr alloy sample) to a maximum value of 19.04 J/mm2 (impact strength of Al-Mg-Si-2.0%Cr alloy sample). After heat treatment, the impact strength of Al-Mg-Si-0%Cr alloy sample increased marginally to 10.09 J/mm2, while that of Al-Mg-Si-2.0%Cr alloy sample decreased slightly to 17.57 J/mm2. The tensile and electrochemical tests revealed that the heat-treated Al-Mg-Si-1.0%Cr alloy sample exhibited the highest tensile strength and lowest corrosion rate of 152 MPa and 0.0014 mm/year, respectively. The microstructural examination further revealed that the inclusion of Cr particles in Al-Mg-Si alloy improved its surface morphology. Al-Mg-Si-1.0%Cr alloy sample was adjudged to possess the best microstructural properties. Therefore, this sample is recommended as a potential material for machine tools and other structural or advanced manufacturing applications.

Microstructural Evolutions and Strengthening Mechanism according to the Aging Temperatures of a High Si Cast Aluminum Alloy

A356 cast aluminum alloy contains 7 at.% Si and 0.3 at.% Mg, producing an approximately 50% eutectic microstructure. This high Si content and various casting conditions play a significant role in strengthening A356 alloy, by controlling the eutectic morphology and precipitates of other intermetallic compounds. Understanding how Si-related precipitates and clusters are soluble in the α-matrix is necessary to provide high strength and fatigue resistance to A356 alloys. The aging heat-treatment temperature in the A356 alloy most likely promotes the formation of these precipitates and clusters. The A356 samples were differently aged at temperatures of 110 oC and 130 oC for 2 h, and were labeled 110A, and 130A, respectively. 110A was found to have improved mechanical properties, such as high strength and elongation, compared to 130A, which may be attributed to the formation of secondary phases in the α-phase matrix. Scanning and transmission electron microscopy and atom probe tomography analyses demonstrated Ti2Si precipitation and various-sized cluster formations in 110A. In contrast, 130A had fewer clusters than 110A. Therefore, different aging heat-treatment temperatures relate to a change in the behavior of atoms, affecting the mechanical properties.

Metallurgical analysis of laser powder bed-fused Al–Si–Mg alloys: Main causes of premature failure

AlSi7Mg and AlSi10Mg are the most used alloys to manufacture Laser Powder Bed Fusion lightweight components. These products have high specific strengths but a sometimes-limited ductility. Several direct aging and T6 heat treatments were applied to as-built alloys to solve the problem and optimise their tensile properties. Investigations about causes of premature failure in AlSi7Mg and AlSi10Mg tensile samples were performed in the as-built, direct aged (200°C × 4h) and T6 (solution heat treatment at 505°C × 4h followed by aging at 175°C) treated conditions. In as built and direct aged samples, laser scan track boundaries affected the crack propagation and, consequently, the elongation values in each analysed condition. Higher elongation values were obtained when the crack predominantly propagates within the heat affected zones and along the laser scan track boundaries. After T6 treatment, defects and needle-like δ-Al5FeSi intermetallic particles are observed contributing to the crack nucleation of samples. The laser scan track boundaries remain after the solution heat treatment and redirect the crack propagation in T6 Al-alloys. The effects of precipitation hardened α-Al matrix on the fracture mechanisms were also investigated in AlSi7Mg samples.

Evolution on the Microstructure and Mechanical Properties of a New Multicomponent Near-Alpha Titanium Alloy after Rolling and Heat Treatments

Near-alpha titanium alloys are widely used in aeroengine blades due to their excellent specific strength and mechanical properties. The mechanical properties of near-α titanium alloys are closely related to the evolution of the microstructure and precipitates. In this paper, the microstructure and mechanical properties of a new type of multi-component near-α titanium alloy sheet after rolling, 700 °C aging, and 800 °C aging were studied. The results show that the strength of the alloy after aging at 700 °C increases from 1156 MPa to 1304 MPa, respectively, but decreases to 1246 MPa with the aging temperature increasing. The ductility of the alloy aged at 700 °C is lower than that of the rolled state, but the ductility increases slightly with the aging temperature increasing. The effect of aging heat treatment on the microstructure and precipitation behavior of alloy plates has been studied and compared with alloys before aging. After heat treatment, the content of primary α decreases from 25% to 5%, respectively. Two kinds of silicide precipitate at different positions, with the large-size spherical silicide being (Ti, Zr, Nb)5Si3, and the small-size fusiform silicide being (Ti, Zr, Nb)6Si3, respectively. Ti3Al was precipitated in the primary α phase, during the aging process. The silicides exhibit the strengthening effect on the alloy, but the effect weakens when the silicides grow up. The loss in ductility is mainly attributed to the precipitation of the α2 phase after aging treatment. However, ductility is improved after applying higher aging temperatures as the size of the α2 phase becomes smaller, and the distribution of them tends to become dispersed.

Comprehensive quality index and map of cast Al alloys according to artificial aging heat treatment conditions using TOPSIS and multiple regression analysis and determination of reasonable heat treatment condition

Some quality indices such as Q, QR, QC and Q0 have been used to evaluate quality level of cast aluminum alloys (Al alloys) based on tensile properties, and quality map has been used to intuitively evaluate the quality level based on the quality index. The previous quality indices and maps lack in evaluating the quality level throughout all the tensile properties, comprehensively. On the other hand, they don’t directly show the quality level according to artificial aging heat treatment condition, while they show the quality level according to the tensile properties. We propose a method to develop comprehensive quality index and map of cast Al alloy according to artificial aging heat treatment condition by using technique for order preference by similarity to ideal solution (TOPSIS) and multiple regression analysis. Moreover, we propose a method to determine a reasonable heat treatment condition by using extremum principle and grid search method. To illustrate the effectiveness, the methods are applied to the cast Al alloy A357. The proposed methods could be widely used to evaluate the comprehensive quality level of the cast Al alloys, and optimize the heat treatment condition.

Cavitation behavior study of the aging heat treated aluminum alloy 7075

Aluminium-based alloy type 7075 is known for its good ductility, high mechanical strength, toughness and high fatigue strength, which is why it is mainly used in the construction of dynamically stressed parts in the structure of airplanes, vehicles and ships. Although it has these qualities, at present its behavior has not been studied at the hydrodynamic stresses that allow it to be used in parts that work in cavitation conditions, such as pump rotors and boat propeller blades. Therefore, the research in this paper highlights the behavior of laminated semi-finished structures and obtained by heat treatment of artificial aging at 180°C, with a maintenance time of one hour. Of the 7075 alloy at the demands generated by the vibrating cavity, created by the standard vibrating device with piezoceramic crystals (frequency of 20 kHz, amplitude of 50 µm and electrical power of 500 W). Analysis based on the curves MDE (t) and MDER (t), of the specific parameters of cavitation erosion MDEmax and MDERs as well as of the macro and microscopic images of the eroded structures of cavitation show that, compared to the delivered state (semi-finished), by the heat treatment applied the microstructure does not change cavitation

Influence of aging heat treatment at 180 °C on cavitation erosion for aluminum alloy type 5083 in cold rolled state

Aluminum-based alloys have wide applicability in the construction of aircraft, vehicles, and ships. Some of their components, during operation, such as the radiators and the rotors of the cooling pumps in the vehicles, and the propellers of fishing and pleasure boats are affected by the abrasive, chemical and cavitational corrosive action of the water. At certain hydrodynamic flow regimes, the most dangerous becomes the corrosion through cavitation. Operation in such regimes inevitably leads to damaging the structure, due to cyclic stresses of the micro-jets and shock waves generated by the implosion of cavitation bubbles. Although the chemical constitution and alloying with other chemical elements increase the mechanical properties, the service life is still limited when operating in high-intensity cavitation flows. Therefore, researchers are looking for solutions to improve this resistance through various treatments, such as bulk heat. Research heading the same direction, but, made on 5083 alloy, is presented in this paper. The results highlight the behavior of a modified structure compared to the semi-fabricated state (obtained by rolling), through three durations regimes (one hours, 12 hours and 24 hours) of aging heat treatment to 180 °C temperature, after hardening treatment at 450 °C. The cavitation tests were performed in the Laboratory of the Polytechnic University of Timisoara, on the standard vibrating device with piezoceramic crystals. The results were expressed by curves and parameters specific to the evaluation of cavitation resistance, and by macro and microscopic images, showing the unique aspects of the connection between the structure and the mechanical properties obtained through heat treatment regimes. Thus, comparison of the results, including with the delivery state (laminated product), shows that the highest resistance is provided by the treatment at 24 hours. At the same time, the erosion, of pitting and caverns type, and differs from one structure to another.

Unusual interface phase transformation during continuous additive manufacturing of maraging steel and Co–30Cr–7Mo alloy

The high strength and hardness of maraging steel (MS1) can be functionally integrated with the thermal stability and toughness of Co–30Cr–7Mo alloy (MP1) through multi-material additive manufacturing via laser powder bed fusion. However, appropriate heat treatment is necessary to stabilize the multi-phase interface post-printing and achieve desired material properties. In the present study, we investigate the effects of solution and aging heat treatment on the interface characteristics and mechanical properties of MS1-MP1 multi-material components. The results reveal that a discontinuous martensitic transformation occurs in the interface after printing due to the combined effects of solute segregation, local stress distribution, and intermixed cellular growth. In contrast, consistent parallel martensite laths were observed after heat treatment due to the homogenized alloying element distribution, extensive residual stress relief and stable interface structure. Furthermore, the mechanical testing results revealed that the tensile strength of the MP1-MS1 alloy was maintained at about 1185 ± 18 MPa before and after heat treatment, complemented by an increase in elongation from 14.7 ± 1.3% to 27.1 ± 2.1%. The microstructure and mechanical properties obtained are then correlated based on phase boundary orientation relationships and simulated martensite start temperatures in different regions along the interface. Based on overall results, it can be concluded that MP1 forms a compatible interface with MS1. Heat treatment can still be performed to improve the strength of MS1 by precipitation strengthening without compromising the strength of MP1 and the MS1-MP1 interface.

Dependence of Tensile Properties and Fracture Behaviors on the Fractions of Continuous and Discontinuous Precipitates in Peak-Aged AZ80A Magnesium Alloy.

After T5 (forging + aging) and different T6 (forging + solution + aging) heat treatments, the AZ80A Mg alloys exhibited microstructures with different fractions of continuous precipitate (CP) regions and discontinuous precipitate (DP) regions. The effects of the fractions of DP regions and CP regions on the tensile properties and fracture behaviors were investigated using microstructural characterizations and analysis. The results showed that increasing the fraction of DP regions enhanced the yield strength and tensile strength at room temperature. However, at the same high temperature, increasing the fractions of DP regions improved the elongation but deteriorated the tensile strength significantly. The different resultant tensile properties at different temperatures were caused by the different precipitation-strengthening effects in the CP and DP regions. The strengthening contribution of the DP regions was more effective at room temperature but became inferior to the effect brought about by the CP regions at high temperatures. Micro-cracks were usually initiated and propagated in the CP regions at room temperature. At high temperatures, however, micro-voids formed more easily in the DP regions, and the fracture path preferred to locate there.

Static and dynamic precipitation phenomena in laser powder bed-fused Ti6Al4V alloy

The present paper investigates static and dynamic precipitation phenomena in the Ti6Al4V alloy produced via laser-powder bed fusion, solubilized at 1050 °C and aged in the range of 450–650 °C. In relation to the distance from the platform on which the samples are disposed during the solution heat treatment, the microstructure varies from α-laths to α-colonies arranged in a Widmanstätten structure. The aging heat treatment at 450 °C promotes the formation of stacking faults into α-laths and the precipitation of α2-Ti3Al phases. SEM and TEM observations reveal that the density of precipitates increases after aging at 500 °C, while coarsening of the α-phase occurs only after aging heat treatment at 600 °C. Vickers microhardness measurements reveal different peak-aging conditions and show that the alloy is unstable at high temperatures (T > 450 °C), both in the case of static and dynamic precipitation phenomena. Only the aging profile at 450 °C shows a constant trend of Vickers microhardness after 4 h of treatment.

Effect of Aging Heat Treatment on Wear Behavior and Microstructure Characterization of Newly Developed Al7075+Ti Alloys.

In this study, Al7075+0%Ti-, Al7075+2%Ti-, Al7075+4%Ti-, and Al7075+8%Ti-reinforced alloys were prepared by melting processes using Al7075 and Al-10%Ti main alloys. All newly produced alloys were subjected to T6 aging heat treatment and some samples were cold rolled at 5% beforehand. The microstructure, mechanical behavior, and dry-wear behavior of the new alloys were examined. Dry-wear tests of all alloys were carried out at a total sliding distance of 1000 m, at a sliding speed of 0.1 m/s, and under a load of 20 N. In the hardness measured after T6 aging heat treatment, the peak hardness of the Al7075+0%Ti-, Al7075+2%Ti-, Al7075+4%Ti-, and Al7075+8%Ti-reinforced alloys was found to be 105.63, 113.60, 122.44, and 140.41 HB, respectively. The secondary phases formed by the addition of Ti to the Al7075 alloy acted as precipitate-nucleation sites during aging heat treatment, further increasing the peak hardness. Compared to the peak hardness of the unrolled Al7075+0%Ti alloy, the increase in the peak hardness of the unrolled and rolled Al7075+8%Ti-reinforced alloys was 34% and 47%, respectively, and this difference in the increase was due to the change in the dislocation density with cold deformation. According to the dry-wear test results, the wear resistance of the Al7075 alloy increased by 108.5% with a reinforcement of 8% Ti. This result can be attributed to the formation of Al, Mg, and Ti-based oxide films during wear, as well as the precipitation hardening, the secondary hardening with acicular and spherical Al3Ti phases, the grain refinement, and solid-solution-hardening mechanisms.

Influence of Silicon Carbide and Graphite Reinforcements and T6 Aging Heat Treatment on the Fatigue Characteristics of AZ91D Magnesium Alloy

Influence of Silicon Carbide and Graphite Reinforcements and T6 Aging Heat Treatment on the Fatigue Characteristics of AZ91D Magnesium Alloy

Investigating microstructural evolution in SolidStir™ extruded oxide dispersion strengthened 14YWT alloy fuel cladding tube

Structural components for extreme environments require advanced materials and manufacturing processes. One such advanced material is oxide dispersion strengthened (ODS) Fe–14 wt.%Cr–3W–0.4Ti–0.3Y2O3 (14YWT), which is developed for components to be used in Gen IV and fusion nuclear reactors. However, the conventional manufacturing processes to produce components, such as fuel cladding tubes, either do not retain the desired microstructural attributes or are costly and less efficient. As a result, a more attractive option is a novel manufacturing process developed on the principle of friction stir welding or processing (FSW/P) and commercially referred to as SolidStir™ Extrusion (SSE). This study used the SSE technique to study the manufacturing and microstructural evolution of a fuel cladding tube made of ODS 14YWT alloy. The cladding extrusion by the SSE technique involved the use of ball-milled 14YWT powders with Y, Ti, and O in the solid solution and the use of a specially designed W-25Re-Hf tool for consolidation and extrusion of the powders. A scanning electron microscope (SEM), electron backscattered diffraction (EBSD), and transmission electron microscope (TEM) were utilized for microstructural characterization. A Keyence microscope captured macrostructural photographs of the extruded tube. EBSD examination of the extruded tube on both transverse and longitudinal cross-sections showed the presence of dynamically recrystallized grains and revealed that the average grain size of the transverse cross-section was smaller than that of the longitudinal cross-section. The texture was weak and consisted of some amount of shear texture. The presence of nano-oxide clusters or precipitates of Y, Ti, and O (pyrochlores) in the extruded tube was determined by TEM. Aging heat treatment caused the average precipitate size to decrease and the density to increase compared to the as-processed condition. The results indicated that SSE is a viable tool for manufacturing fuel cladding tubes with the desired microstructural attributes.

Tuning the microstructure and mechanical properties of AlSi10Mg alloy via in-situ heat-treatments in laser powder bed fusion

Together, advanced technologies and metallic materials rapidly progress in the field of Laser Powder Bed Fusion (PBF-LB) additive manufacturing (AM). Although PBF-LB drastically shortens the design-to-manufacture time, post-processing operations on metal parts, including heat-treatments, are often labour intensive and time-consuming. Therefore, we assess the feasibility of conductingin-situ heat-treatments during PBF-LB of AlSi10Mg parts. A build plate heated at set temperatures up to 500 °C was employed while printing for 10–13 h to tune the material's microstructure. For comparison, a batch of samples was printed at 220 °C and 500 °C with a printing time of 4–6 h, which was subsequently solution heat-treated. The experimental results showed that increasing the printing time from 5 h to 11 h while printing at 220 °C resulted in an in-situ direct aging heat-treatment with an actual increment of hardness and strength. Printing at 300 °C induced a significant Al lattice relaxation and consequent in-situ stress relieving of the as-built parts. Lastly, the study shows that in-situsolution heat-treatment is possible when using build plate temperatures between 450 °C and 500 °C for 11 h, although a reduction in ductility (−36%) occurs, as compared to conventionally solution heat-treated counterparts.

Effects of heat treatment on the corrosion behavior and mechanical properties of aluminum alloy 2024

Aluminum alloy, specifically 2024, is extensively utilized in the automotive and aerospace industries due to its light weight and superior mechanical properties. This study explores the corrosion behavior and mechanical characteristics of this alloy following quenching and aging heat treatments. Accelerated corrosion tests involved immersing samples in a salt spray chamber with a 5% NaCl solution, maintained at a temperature of 40 °C with a neutral pH. The alloy's microstructure and corrosion behavior were examined before and after the corrosion test, which included a heat treatment at 495 °C and aging for five days. Multiple tests, such as Vickers microhardness, optical microscopy, scanning electron microscopy (SEM), and tensile tests were performed. The surface characteristics, specifically the refined microstructure and residual stresses, were analyzed and their impact on localized corrosion was evaluated. The maximum strength value rose from 411 MPa to 512 MPa, and elongation increased correspondingly. Concerning corrosion sensitivity, a reduction was observed in the following order: AA2024-T3 (natural condition), AA2024-T3 (tempered condition), and AA2024-T3 (aged condition). The aged treatment appeared to enhance corrosion resistance, potentially due to the minimized size of corrosion products observed post-etching in various regions.

Deformation mechanism of highly textured Alnico magnets

Deformed Alnico magnets were prepared by hot isostatic pressing (HIP) spherical powders and hot rolling (HR), and the hot-rolled magnets were solution-treated at 1250 ℃, magnetic heat treated at 835 ℃, and three-stage aged at 600 – 500 ℃, respectively. The results show that Alnico spherical powder comprises 77.5% α phase, 8.6% α1 phase, and 13.9% α2 phase. The HIP magnet has spinodal decomposed during the preparation, and HR improved α content. The magnet has spinodal decomposed thoroughly after magnetic heat treatment (MHT) and aging heat treatment (AHT), composed of 62.1% α1 phase with a B2 structure and 37.9% Fe2NiAl-type α2 phase with the L21 structure. Moreover, the HIP and HR magnet preferentially produces the< 100 > texture, which is also enhanced along the< 211 > directions. The preferred deformation of the α1 phase is carried out under the synergistic action of the α2 phase. The HIP deformation mechanism is that composition diffusion and structural transformation are carried out in different stages, resulting in four kinds of two-phase structures. The rolling deformation mechanism is that the grains parallel or nearly parallel to the rolling direction are directly rolled into lath-like ones, and four kinds of microstructures are formed in the grains. Compared to the HIP magnet, the MHT and AHT promote the formation of the fibrous structure, and the maximum aspect ratio of α1 phase reaches ∼35:1. The coercivity of the heat-treated magnet increased by 160.9%, and the remanence and magnetic energy product also increased simultaneously.

Effects of additive manufacturing processes and isothermal aging on the microstructure and properties of 13-8 Mo precipitation hardening martensitic stainless steel

The objective of this study is to evaluate the effect of AM process on the microstructure and properties of PH 13-8 Mo steel in the as-printed and aged conditions. Samples were produced by both laser powder bed fusion (L-PBF) and arc directed energy deposition (arc-DED) and characterized in both the as-printed and direct aged (530 °C, 3 hrs) conditions. The as-printed L-PBF sample was characterized by a nearly fully martensitic microstructure, while the as-printed arc-DED microstructure included coarser lath martensite, 2.3 vol.% retained austenite, and δ-ferrite. However, the hardness of the as-printed arc-DED sample (401.0 HV1) was greater than the as-printed L-PBF (347.7 HV1), due to precipitation of β-NiAl particles in the as-printed arc-DED condition. Aging of the L-PBF sample resulted in microstructure refinement, precipitation of β-NiAl particles, and a corresponding increase in hardness to 508.3 HV1. Conversely, aging the arc-DED sample resulted in the formation of a large amount of reverted austenite (7.2 vol.%), Cr23C6 particles, as well as β-NiAl particles, but was unable to remove the δ-ferrite grains. Consequently, the hardness of the aged arc-DED sample was similar to the as-printed value (428.3 HV1). It is concluded that the selection of the AM process has an important effect on the microstructure and properties of PH 13-8 Mo steel, and that a single-step direct aging heat treatment is suitable for samples produced by L-PBF but not arc-DED.

Investigation of structural, electrical and tribological properties of duplex surface treated and aged Cu−Cr−Zr alloy

AbstractIn this study, Cu−Cr−Zr alloy specimens were first subjected to aging heat treatment at 500 °C for two different durations (2 hours and 4 hours). Three different coating processes (silver, silver/copper duplex, and copper/silver duplex) were applied to the aged specimens using the physical vapor deposition method. Tensile test, microhardness measurement, wear test, electrical conductivity measurement and structural analysis (x‐ray diffraction and scanning electron microscope) were applied to the specimens. After the aging processes, the highest hardness and strength values of the Cu−Cr−Zr alloy were obtained in the specimens that were aged at 500 °C for 4 hours. When the wear resistance and electrical conductivity of the coated specimens were examined, it was determined that the specimens with duplex surface treatment performed better.

PBF (Powder Bed Fusion)와 DED (Directed Energy Deposition)의 연속 공정으로 적층제조된 630 스테인레스강의 마모 거동에 관한 연구

Hybrid additive manufacturing (AM) refers to a combination of two metal AM techniques: material deposition by powder bed fusion (PBF) and additional building by directed energy deposition (DED). This study focused on different characteristics in accordance with relative deposition directions of PBF and DED during hybrid AM production. Characteristics of the sample fabricated by hybrid AM (i.e., hybrid sample) were compared with those of the sample fabricated by PBF or DED. Ferrite was dominant in the microstructure of PBF deposits with very fine retained austenite observed locally. In contrast, lath martensite and retained austenite were formed uniformly in the microstructure of DED deposits. Different microstructures in the two processes were attributed to differences of cooling rate. In DED deposits, microhardness was significantly decreased owing to a high retained austenite fraction. However, in the hybrid sample, microhardness was rapidly increased in the HAZ owing to aging heat treatment for long-term deposition. Principal wear mechanisms of PBF and DED samples were oxidative wear and plastic deformation, respectively.