Effect of Intermediate Heat Treatment Temperature on Microstructure and Notch Sensitivity of Laser Solid Formed Inconel 718 Superalloy

Inconel 718 superalloys deposited by laser solid forming （LSF） were heat treated with solution treatment,intermediate heat treatment （IHT） and two-stage aging treatment in sequence （SITA heat treatment）.The effect of IHT temperature on microstructure,tensile property and notch sensitivity of LSFed Inconel 718 superalloy at 500 ℃ were investigated.As-deposited columnar grains have transformed to equiaxed grains and the grains were refined due to the recrystallization during the SITA heat treatment.It is found that the size and amount of δ phase dispersed at grain boundaries decreased with the increasing of IHT temperature,and δ phase disappeared when the IHT temperature reached 1 020 ℃.The ultimate tensile strength （UTS） and yield strength （YS） of smooth samples increased to a maximum when the IHT temperature reached 980 ℃ and then decreased slightly to a minimum when the IHT temperature was 1 000 ℃,and followed by slight increasing again till the IHT temperature reached 1 020 ℃,resulted from the competition of precipitation strengthening effect of γ″ and γ＇ phase and the grain boundary weakening effect caused by the gradual disappearance of δ phase with increasing the IHT temperature.The notch sensitivity factor （qe） decreased but still greater than 1 as the IHT temperature increased,which is attributed to the decrease of the size and amount of δ precipitation.

The effects of heat treatment on microfluidic devices fabricated in silica glass by femtosecond lasers

We fabricated complex microfluidic devices in silica glass by water-assisted femtosecond laser ablation and sub- sequent heat treatment. The experimental results show that after heat treatment, the diameter of the microehannels is significantly reduced and the internal surface roughness is improved. The diameters of the fabricated microehannels can be modulated by changing the annealing temperature and the annealing time. During annealing, the temperature affects the diameter and shape of the protrusions in microfluidic devices very strongly, and these changes are mainly caused by uniform expansion and the action of surface tension.

Influence of post-weld heat treatment on the microstructure and hardness of laser weld seams on hot-rolled TRIP 800 steel

The transformation induced plasticity (TRIP) steels effect occurs because of the martensitic transformation of retained austenite during plastic deformation,and it provides the steel with excellent strength and ductility.While welding remains a vital part of auto body manufacturing,the weldability of TRIP steels is problematic,and this prevents its adoption for many applications in the automotive industry.This present work studies the effects of welding and post-weld heat treatment on the microstructure of TRIP steels.It is found that the microstructures of the fusion zone and the heat affected zone (HAZ) are changed after high-temperature heat treatment.Hardness tests revealed that fusion zone hardness decreased with increasing of temperatures in the post-weld heat treatment on the laser weld seam.The rolling performance of the welding seam and the seam of post-weld heat treatment were also studied.

Microstructure and mechanical properties of laser additive manufactured novel titanium alloy after heat treatment

A novel α+β titanium alloy with multi-alloying addition was designed based on the cluster formula 12[Al-Ti_(12)](AlTi_(2))+5[Al-Ti_(14)](AlV_(1.2)Mo_(0.6)Nb_(0.2))which was derived from Ti-6Al-4V.The nominal composition of this novel alloy was determined as Ti-6.83Al-2.28V-2.14Mo-0.69Nb-6.79Zr.In this study,the novel alloy and Ti-6Al-4V alloy samples were prepared by laser additive manufacturing.The microstructure,micro-hardness,room/high temperature tensile properties of the as-deposited samples were investigated.Compared to Ti-6Al-4V,the novel alloy has much higher room and high temperature(600℃)tensile strengths,which are 1,427.5 MPa and 642.2 MPa,respectively;however,it has a much lower elongation(3.2%)at room temperature because of the finer microstructure.To improve the elongation of the novel alloy,heat treatment was used.After solution at 960℃ or 970℃ for 1 h followed by air cooling and aging at 550℃ for 4 h followed by air cooling,a unique bi-modal microstructure which contains crab-like primaryαand residual β phase is obtained,improving the compression elongation by 80.9% compared to the as-deposited samples.The novel alloy can be used as a high-temperature and high-strength candidate for laser additive manufacturing.

The Effects of Different Post-Heat Treatments on Rolling Contact Fatigue Behaviors of Direct Laser Cladding Inconel 625 Coatings

In this paper,the microstructures and rolling contact fatigue behaviors of laser cladding Inconel 625 coatings with or without post-heat treatments were analyzed.The results revealed that the fatigue resistance of the laser cladding coating after any post-heat treatment was worse than that of the as-deposited coating.First,through the finite element analysis,the distribution of stress along the thickness direction of the coating was obtained,and it was concluded that the bonding interface between the coating and the matrix had little effect on the fatigue properties of the coating.Then X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS)were used to analyze the microstructure and failure morphology.The results revealed that the subsurface failure morphology of the coatings showed a consistent correlation with rolling fatigue property after different heat treatments.The TCP phase and carbides have been shown in the laser cladding coating.The coating after stress relieved annealing exhibited chain-shaped granular carbides on the grain boundaries which could accelerate crack propagation.The aging heat treatment made small amounts of Laves phase dissolved in the coating,while the dispersed phase was precipitated which could result in the formation of pores.And the solution treatment made large amounts of Laves phase dissolved,while the rod-shape brittle phases were generated which was easy to fracture and contribute to crack initiation and spalling.

Effects of laser heat treatment on salt spray corrosion of 1Cr5Mo heat resistant steel welding joints

The surface of 1Cr5 Mo heat-resistant steel welding joint was processed with CO2 laser, and the corrosion behaviors before and after laser heat treatment(LHT) were investigated in the salt spray corrosion environments. The microstructures, phases, residual stresses and retained austenite content of 1Cr5 Mo steel welding joint before and after LHT were analyzed with optical microscope and X-ray diffraction, respectively. The cracking morphologies and chemical compositions of corrosion products after salt spray corrosion were analyzed with field emission scanning electron microscopy(FESEM) and energy disperse spectroscopy(EDS), respectively, the polarization curves were measured on a PS-268 A type electrochemical workstation, and the mechanism of corrosion resistance by LHT was investigated as well. The results show that the passive film of original sample is destroyed owing to the corrosive media penetrating into the subsurface, resulting in the redox reaction. The content of residual austenite in the surface and the self-corrosion potential are increased by LHT, which is contributed to improving the capability of salt spray corrosion resistance.

Effect of post-weld heat treatment on microstructure and properties of Ti-23Al-17Nb alloy laser beam welding joints

The mechanical properties of Ti-23Al-17Nb (mole fraction,%) laser beam welding alloy joint at room temperature are comparable to that of the base materials.However,the strength and ductility of the as-welded joint deteriorate seriously after high temperature circulation.The effect of post-welded heat treatment on the microstructure and mechanical properties of the joint was investigated.The heat treatment was taken at 980 ℃ for 1.5 h,then furnace cooling and air cooling were performed separately.The results indicate that proper post-welded heat treatment improves the ductility of the joint at high temperature.

Effects of Heat Treatment on Microstructure and Hardness of Laser Clad NiWCRE Alloy Layer

The effects of heat treatment on tnicrostructure and hardness of laser surface-clad Ni2 !+20%WC+0.5%CeO2 on the heat-resistant cast iron were investigated by means of X-ray diffraction(XRD), transmission electron microscope(TEM) and microhardness test. The experimental results showed that heat-treating at 500’C has no effect on microstructure and hardness of the layers. Although the phase composition of the layers heat-treated at 700°C and 800°C remain unchanged, more Ni3B and N14B3 phases are precipitated on the matrix of the cladding layer, the metastable phase—M7C3 is transformed into steady phase—M23C6, and the precipitated phases coarsened.

Heat-treated microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming （LSF） Ti-6Al-4V alloy were investigated The influences of the temperature and time of solution treatment and aging treatment were analyzed. The results show that the microstructure of LSFed samples consists of Widmanstatten α laths and a little acicular in columnar prior β grains with an average grain width of 300 μm, which grow epitaxiaUy from the substrate along the deposition direction （27）. Solution treatment had an important effect on the width, aspect ratio, and volmne fraction of primary and secondary a laths, and aging treatment mainly affects the aspect ratio and volume fraction of primary α laths and the width and volume fraction of secondary a laths. Globular a phase was first observed in LSFed samples when the samples were heat treated with solution treatment （950℃, 8 h/air cooling （AC）） or with solution treatment （950℃, 1 h/AC） and aging treatment （550℃, above 8 h/AC）, respectively. The coarsening and globularization mechanisms of a phase in LSFed Ti-6Al-4V alloy during heat treatment were presented. To obtain good integrated mechanical properties for LSFed Ti-6Al-4V alloys, an optimized heat treatment regimen was suggested.

Designing High-Porosity Porous Structures with Complex Geometries for Enhanced Thermal Conductivity Using Selective Laser Melting and Heat Treatment

Rapid advancements in the aerospace industry necessitate the development of unified,lightweight and thermally conductive structures.Integrating complex geometries,including bionic and porous structures,is paramount in thermally conductive structures to attain improved thermal conductivity.The design of two high-porosity porous lattice structures was inspired by pomelo peel structure,using Voronoi parametric design.By combining characteristic elements of two high-porostructuressity porous lattice structures designed,a novel high-porosity porous gradient structure is created.This structure is based on gradient design.Utilizing selective laser melting(SLM),fabrication comprises three.Steady-state thermal characteristics are evaluated via finite element analysis(FEA).The experimental thermal conductivity measurements correlate well with simulation results,validating the sequence of K_L as the highest,followed by D_K_L and then D_L.Heat treatment significantly improves thermal conductivity,enhancing the base material by about 45.6%and porous structured samples by approximately 43.7%.

Effect of Heat Treatment on Microstructure and Mechanical Behavior of Cu-Bearing 316L Stainless Steel Produced by Selective Laser Melting

Cu-bearing stainless steels(SSs)with high strength,excellent plasticity,and effective antimicrobial properties hold significant potential for applications in the marine industry.In this study,Cu-bearing SSs with copper ranging from 0 to 6.0 wt%were successfully prepared using selective laser melting(SLM)technology.For the Cu-bearing SSs with different copper contents,the effect of heat treatment on the microstructural and mechanical behaviors was studied systematically.Microstructural observations revealed that the subgrain size of Cu-bearing SSs increased with heat treatment at 500℃ and 700℃ for 6 h.Furthermore,the tensile strength and elongation increased after the heat treatment temperature due to the combined effect of dislocations,twins,andε-Cu precipitated phases.Notably,after heat treatment at 700℃,the SLM4.5Cu sample exhibited an abnormal rise in tensile strength and elongation.This finding suggests that the diffusion strengthening caused byε-Cu precipitates exceeded the stacking fault energy.Consequently,the tensile strength and elongation reached 693.32 MPa and 56.94%,respectively.This work provides an efficient approach for preparing Cu-bearing SSs with exceptional strength and plasticity.

Effect of Heat Treatment on Gradient Microstructure and Tensile Property of Laser Powder Bed Fusion Fabricated 15-5 Precipitation Hardening Stainless Steel

This work investigated the gradient microstructure evolution and tensile property of LPBF fabricated 15-5 precipitation hardening stainless steel in post-process direct ageing(DA)and solution treating&ageing(STA).The varied microstructures for austenite and small-sized oxide inclusions at different sample heights in the as-built(AB)condition was generally preserved after DA treatment.However,austenite was almost disappeared,and oxide particle grew significantly after the STA treatment.As a result,the tensile property differences in sample top and bottom for AB and DA conditions did not occur in the STA samples.For the influence of post-process heat treatment,the STA condition had the highest yield strength due to the highest volume fraction of nano-sized Cu precipitates.However,the DA specimen had the highest ultimate tensile strength and elongation owing to the considerable amount of austenite phase and associated transformation induced plasticity effect.

Effect of heat treatment on microstructure and properties of VG10 and 3Cr13 dissimilar welded joints

Through laser swing welding of dissimilar steels,the microstructure and properties of welded joints of dissimilar steels under different heat treatment processes were investigated.In the test,the equilibrium phase diagrams of the base materials 3Cr13 and VG10 were calculated by JMATPro software.The microstructures of the different regions of the welded joints after the original and heat treatment were analyzed by XRD and SEM,and the changes of the microhardness were tested.The test results show that a martensite-like structure is generated at the base material on the 3Cr13 side of the original welded joint,and a non-convective mixing zone exists in the fusion zone on the VG10 side.At this location,a block-like,island-like structure is embedded in the base material.There were lamellar carbide formation on this structure.After heat treatment,the amount of carbides in the welded joints is reduced,but the primary carbides in the VG10 base metal are difficult to eliminate by heat treatment.In addition,the lamellar carbides in the VG10 side fusion zone are polymerized to form network carbides.The hardness of the base metal near the fusion line on both sides of the original welded joint is relatively large,and the hardness of the heat affected zone gradually decreases with increasing distance from the center of the weld.After heat treatment,the overall hardness of the welded joint has increased significantly.Among them,the hardness increase is greatest at the quenching temperature of 1050°C,and VG10 can reach about 830 HV.

Hardness Profile Prediction for a 4340 Steel Spline Shaft Heat Treated by Laser Using a 3D Modeling and Experimental Validation

Laser surface transformation hardening becomes one of the most effective processes used to improve wear and fatigue resistance of mechanical parts. In this process, the material physicochemical properties and the heating system parameters have significant effects on the characteristics of the hardened surface. To appropriately exploit the benefits presented by the laser surface hardening, it is necessary to develop a comprehensive strategy to control the process variables in order to produce desired hardened surface attributes without being forced to use the traditional and fastidious trial and error procedures. The paper presents a study of hardness profile predictive modeling and experimental validation for spline shafts using a 3D model. The proposed approach is based on thermal and metallurgical simulations, experimental investigations and statistical analysis to build the prediction model. The simulation of the hardening process is carried out using 3D finite element model on commercial software. The model is used to estimate the temperature distribution and the hardness profile attributes for various hardening parameters, such as laser power, shaft rotation speed and scanning speed. The experimental calibration and validation of the model are performed on a 3 kW Nd:Yag laser system using a structured experimental design and confirmed statistical analysis tools. The results reveal that the model can provide not only a consistent and accurate prediction of temperature distribution and hardness profile characteristics under variable hardening parameters and conditions but also a comprehensive and quantitative analysis of process parameters effects. The modelling results show a great concordance between predicted and measured values for the dimensions of hardened zones.

LASER HEAT TREATING RESEARCH OF THREE KINDS OF HIGH SPEED STEEL

After laser quenching and tempering of three kinds of annealed tool high-speed steel(W18Cr-4V, W9Mo3Cr4V1, W6Mo5Cr4V2) test samples, the microhardness measurer was used to test the samples and some problems, such as the hardness and depth of hardening-quenching layer were analyzed. Furthermore, after laser quenching and tempering of the quenched and three-time tempered high-speed steel (W18Cr4V) and its hardness analyzing, different results of laser-quenching samples were obtained under different initial heat-treating.

Corrosion Testing of a Heat Treated 316 L Functional Part Produced by Selective Laser Melting

Selective Laser Melting (SLM) shows a big potential among metal additive manufacturing (AM) technologies. However, the large thermal gradients and the local melting and solidification processes of SLM result in the presence of a significant amount of residual stresses in the as built parts. These internal stresses will not only affect mechanical properties, but also increase the risk of Stress Corrosion Cracking (SCC). A twister used in an air extraction pump of a condenser to create a swirl in the water, was chosen as a candidate component to be produced by SLM in 316 L stainless steel. Since the main expected damage mechanism of this component in service is corrosion, corrosion tests were carried out on an as-built twister as well as on heat treated components. It was shown that a low temperature heat treatment at 450℃ had only a limited effect on the residual stress reduction and concomitant corrosion properties, while the internal stresses were significantly reduced when a high temperature heat treatment at 950℃ was applied. Furthermore, a specific stress corrosion sensitivity test proved to be a useful tool to evaluate the internal stress distribution in a specific component.

热处理对激光粉末床熔融AlSi10Mg合金热物理性能的影响

采用激光粉末床熔融(laser powder bed fusion,LPBF)法成功制备AlSi10Mg合金样品,研究130℃/4 h时效处理、236℃/10 h退火处理和540℃/1 h固溶处理三种热处理工艺对AlSi10Mg合金样品的微观组织的影响,以及热处理后AlSi10Mg合金在室温~400℃的温度范围内热膨胀系数和热导率演变规律。结果表明:时效处理后铝基体中析出球状的Si颗粒,仍然保留完整的网状共晶硅组织;退火后,网状共晶硅完全消失,球化Si颗粒均匀分布在基体中;固溶处理后出现大的块状Si颗粒,尺寸在1~3μm;经过热处理之后AlSi10Mg合金的热物理性能均优于打印态。退火处理后的合金样品在室温到400℃的热膨胀系数为1.64×10^(−5)~2.1×10^(−5)℃^(−1),平均热导率为179.6 W·m^(−1)·K^(−1),性能优于时效处理和固溶处理。

热处理对选区激光熔化Al-Mn-Mg-Sc-Zr合金力学性能和腐蚀行为的影响

以Al-4.77Mn-1.37Mg-0.67Sc-0.25Zr(质量分数,%)合金粉末为原料,在激光功率330 W和扫描速率700 mm/s下进行选区激光熔化(Selective laser melting,SLM)形成SLM Al-Mn-Mg-Sc-Zr合金,结合慢应变速率拉伸实验、电化学测试、析氢浸泡实验及显微组织表征手段,分析了(350℃,8 h)热处理对SLM Al-Mn-Mg-Sc-Zr合金力学性能和腐蚀行为的影响。结果表明:SLM Al-Mn-Mg-Sc-Zr合金力学性能优异,抗拉强度、屈服强度和伸长率分别为423 MPa、376 MPa和25.1%。热处理后,SLM Al-Mn-Mg-Sc-Zr合金晶内析出大量针棒状纳米Al_(6)Mn相,抗拉强度和屈服强度分别提升至509 MPa和478 MPa。此外,SLM Al-Mn-Mg-Sc-Zr合金具有良好的耐蚀性能,热处理可以促进SLM Al-Mn-Mg-Sc-Zr合金的钝化,在-0.5 V极化电位时出现钝化台阶,降低SLM Al-Mn-Mg-Sc-Zr合金的电流密度,增加SLM Al-Mn-Mg-Sc-Zr合金的阳极极化率,使SLM Al-Mn-Mg-Sc-Zr合金的平均析氢速率从0.242 mL/(cm^(2)·h)降至0.216 mL/(cm^(2)·h),应力腐蚀敏感因子从3.379%降至0.405%。与此同时,热处理也促进了晶内微米富Si相以及晶界富Mn相和Mg相的析出,增加了SLM Al-Mn-Mg-Sc-Zr合金点蚀形核位置,增大了SLM Al-Mn-Mg-Sc-Zr合金的晶界电化学成分非均匀性,降低了SLM Al-Mn-Mg-Sc-Zr合金的点蚀和晶间腐蚀抗力。

激光增材制造与连接GH4169合金的热处理工艺研究

采用激光增材制造技术制备了GH4169合金母材样品,并采用相同的工艺参数实现了母材的激光增材连接,检测了不同热处理状态下合金的拉伸性能,分析了性能改变的内在机理。结果表明:凭借激光增材制造技术热影响区小的优势,热处理前后母材与连接区域处微观组织的演变基本一致。沉积态合金呈典型的柱状晶组织,且二次枝晶并不发达,γ+Laves共晶相呈条带状和岛链状沿晶界分布;均匀化+固溶处理后Laves相发生分解并回溶入基体,并伴随着柱晶的粗化;当进行双重时效处理时Laves相的分布状态发生改变。不同热处理工艺试样的拉伸性能均高于同合金铸态指标,热处理对Laves相的含量和分布状态的改变是影响其强度和塑性的主要因素。

热处理对选区激光熔化Co-Cr合金微观组织与力学性能的影响

热处理不仅可以消除激光增材制造材过程中的热应力,还可以调控材料组织结构和力学性能。本文研究了选区激光熔化Co-Cr合金微观组织在不同热处理条件下的变化及其相应的力学性能。研究发现,打印态下合金组织为γ奥氏体,基体中存在大量层错和亚晶界组织,以及少量四方σ-CoCr沉淀相;在1150℃下保温1 h,发生γ-ε转变,ε马氏体含量为10.4%(V/V),同时沉淀相由四方σ相转变为六方Co_(3)W(Mo)_(2)Si相;再经过800℃处理2 h后,马氏体含量进一步增加至15.5%(V/V),同时沉淀相数量增加且尺寸增大。热处理后的沉淀相对力学性能影响显著,材料的硬度从31 HRC提高至38 HRC,屈服强度从848 MPa提高至1119 MPa。本研究可以为研究激光选区熔化Co基合金组织与性能调控提供参考。