Influence of heat treatments on microstructure and mechanical properties of laser additive manufacturing Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy

The effect of heat treatments on laser additive manufacturing(LAM)Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy(TC17)was studied aiming to optimize its microstructure and mechanical properties.The as-deposited sample exhibits features of a mixed priorβgrain structure consisting of equiaxed and columnar grains,intragranular ultra-fineαlaths and numerous continuous grain boundaryα(αGB).After being pre-annealed inα+βregion(840°C)and standard solution and aging treated,the continuousαGB becomes coarser and the precipitate free zone(PFZ)nearby theαGB transforms into a zone filled with ultra-fine secondaryα(αS)but no primaryα(αP).When pre-annealed in singleβregion(910°C),allαphases transform intoβphase and the alloying elements distribute uniformly near the grain boundary.DiscontinuousαGB and uniform mixture ofαP andαS near grain boundary form after subsequent solution and aging treatment.The two heat treatments can improve the tensile mechanical properties of LAM TC17to satisfy the aviation standard for TC17.

Influence of heat treatment on microstructure and mechanical properties of FeCrNi coating produced by laser cladding

The FeCrNi alloy powders were used on the dovetail groove of FV520B steel to fabricate the multilayer laser cladding layers. The effects of heat treatment on the microstructure and mechanical properties of FeCrNi layers were investigated. The results showed that the heat treatment at the temperature ranged from 1073 to 1273 K refined the grains of the substrate materials and removed the soft zone of hardness between the fused zone (FZ) and base material (BM) effectively mainly due to a secondary quench of heat treatment. When the temperature of heat treatment was 1073 K, the maximum ultimate tensile strength (UTS) values of the laser cladding component were obtained. However, the heat treatment at high temperature had a bad effect on wear resistance of coatings at some extent.

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.

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.

Effect of solution treatment on the microstructure,phase transformation behavior and functional properties of NiTiNb ternary shape memory alloys fabricated via laser powder bed fusion in-situ alloying

Post-heat treatment is commonly employed to improve the microstructural homogeneity and enhance the mechanical performances of the additively manufactured metallic materials.In this work,a ternary(NiTi)91Nb9(at.%)shape memory alloy was produced by laser powder bed fusion(L-PBF)using pre-alloyed NiTi and elemental Nb powders.The effect of solution treatment on the microstructure,phase transformation behavior and mechanical/functional performances was investigated.The in-situ alloyed(NiTi)91Nb9 alloy exhibits a submicron cellular-dendritic structure surrounding the supersaturated B2-NiTi matrix.Upon high-temperature(1273 K)solution treatment,Nb-rich precipitates were precipitated from the supersaturated matrix.The fragmentation and spheroidization of the NiTi/Nb eutectics occurred during solution treatment,leading to a morphological transition from mesh-like into rod-like and sphere-like.Coarsening of theβ-Nb phases occurred with increasing holding time.The martensite transformation temperature increases after solution treatment,mainly attributed to:(i)reduced lattice distortion due to the Nb expulsion from the supersaturated B2-NiTi,and(ii)the Ti expulsion from theβ-Nb phases that lowers the ratio Ni/Ti in the B2-NiTi matrix,which resulted from the microstructure changes from non-equilibrium to equilibrium state.The thermal hysteresis of the solutionized alloys is around 145 K after 20%pre-deformation,which is comparable to the conventional NiTiNb alloys.A short-term solution treatment(i.e.at 1273 K for 30 min)enhances the ductility and strength of the as-printed specimen,with the increase of fracture stress from(613±19)MPa to(781±20)MPa and the increase of fracture strain from(7.6±0.1)%to(9.5±0.4)%.Both the as-printed and solutionized samples exhibit good tensile shape memory effects with recovery rates>90%.This work suggests that post-process heat treatment is essential to optimize the microstructure and improve the mechanical performances of the L-PBF in-situ alloyed parts.

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.

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.

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.

Tailorable microstructure and mechanical properties of selective laser melted TiB/Ti-6Al-4V composite by heat treatment

This paper systematically investigated the effect of solution and artificial aging heat treatments on the microstructural evolution and mechanical properties of TiB/Ti-6Al-4V composites in situ fabricated by selective laser melting.The results showed that the fully martensite microstructure with TiB clusters of the as-built samples was transformed into lamellarα+βmicrostructure with TiB strips after solution heat treatment.With increasing the temperature,theαlaths and TiB particles coarsened and theβvolume fraction increased.After aging heat treatment,βvolume fraction decreased and TiB had no obvious changes.A superior combination of the yield strength of(1146.8±28.2)MPa and even higher plasticity and ultimate compressive strength((1680.1±18.3)MPa)than the as-built ones was obtained by solution heat treatment at 1000℃+water quenching and aging at 600℃for 6 hþair cooling.

Effect of cyclic heat treatment on microstructure and mechanical properties of laser aided additive manufacturing Ti-6Al-2Sn-4Zr-2Mo alloy

Globularαphases can significantly improve the ductility of titanium alloys.Cyclic heat treatment(CHT)has been proved to be an effective way to induce the formation of globularαphases inα+βtitanium alloy Ti-6Al-4V fabricated by laser aided additive manufacturing(LAAM).However,there is no prior research reporting methods for obtaining globularαphases in LAAM-built near-αtitanium alloys.This work investigated the cyclic heat treatment(CHT)procedures suitable for the LAAM-built near-αtitanium alloy Ti-6Al-2Sn-4Zr-2Mo(Ti6242)to attain the globularαphases.The results show that 980℃ is the most suitable upper temperature limit for CHT.However,it is difficult to achieve a high volume fraction of the globularαphases in the LAAM-built Ti6242 alloys through CHT,which is ascribed to the low composition gradient caused by moreα-stabilizing elements and fewerβ-stabilizing elements.The as-built sample demonstrated elongation of 6.3%,which is lower than the AMS 4919J standard(elongation≥10%).After 980℃ CHT and 980℃ CHT with solution heat-treatment,the formation of the globularαphases significantly increased the elongation to 13.5%and 12.9%,respectively.Although the mechanical strength is reduced after heat-treatment,the room-temperature tensile properties still exceed the AMS 4919J standard.Fractography examination showed that the as-built sample exhibited a mixed brittle and ductile fracture behavior,while the 980℃ CHT and 980℃ CHT with solution heat-treated samples displayed ductile fracture.

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.

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.

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.

Theoretical analysis and numerical simulation of the impulse delivering from laser-produced plasma to solid target

A plasma is produced in air by using a high-intensity Q-switch Nd：YAG pulsed laser to irradiate a solid target, and the impulses delivering from the plasma to the target are measured at different laser power densities. Analysing the formation process of laser plasma and the laser supported detonation wave （LSDW） and using fluid mechanics theory and Pirri＇s methods, an approximately theoretical solution of the impulse delivering from the plasma to the target under our experimental condition is found. Furthermore, according to the formation time of plasma and the variation of pressure in plasma in a non-equilibrium state, a physical model of the interaction between the pulse laser and the solid target is developed. The plasma evolutions with time during and after the laser pulse irradiating the target are simulated numerically by using a three-dimensional difference scheme. And the numerical solutions of the impulse delivering from the plasma to the target are obtained. A comparison among the theoretical, numerical and experimental results and their analyses are performed. The experimental results are explained reasonably. The consistency between numerical results and experimental results implies that the numerical calculation model used in this paper can well describe the mechanical action of the laser on the target.

Influence of secondary treatment with CO_2 laser irradiation for mitigation site on fused silica surface

The ablation debris and raised rim, as well as residual stress and deep crater will be formed during the mitigation of damage site with a CO2 laser irradiation on fused silica surface, which greatly affects the laser damage resistance of optics. In this study, the experimental study combined with numerical simulation is utilized to investigate the effect of the secondary treatment on a mitigated site by CO2laser irradiation. The results indicate that the ablation debris and the raised rim can be completely eliminated and the depth of crater can be reduced. Notable results show that the residual stress of the mitigation site after treatment will reduce two-thirds of the original stress. Finally, the elimination and the controlling mechanism of secondary treatment on the debris and raised rim, as well as the reasons for changing the profile and stress are analyzed. The results can provide a reference for the optimization treatment of mitigation sites by CO2laser secondary treatment.

Numerical simulation of temperature field in deep penetration laser welding of 5A06 aluminum cylinder

Deep penetration laser welding temperature field of 5A06 aluminum alloy canister structure was simulated using the surface-body combination heat source model by ANSYS, which was made up of Gauss surface heat source model and Gauss revolved body heat source model. Convection, radiation and conduction were all con,sidereal during the simulation process. The thermal cycle curves of the points both on the shell outer surface and in the seam thickness direction were calculated. Simulated results agreed well with the experiment results. It concluded that the surface-body combination heat source model was fit for the temperature field simulation of deep penetration laser welding of the aluminum alloy canister structure. This method was proved to be an efficient way to predict the shape and dimension of welded joint for deep penetration laser welding of the aluminum alloy canister structure.

High Heat Flux Testing of B_4C/Cu and SiC/Cu Functionally Graded Materials Simulated by Laser and Electron Beam

B4C, SiC and C, Cu functionally graded-materials (FGMs) have been developed by plasma spraying and hot pressing. Their high-heat flux properties have been investigated by high energy laser and electron beam for the simulation of plasma disruption process of the future fusion reactors, And a study on eroded products of B4C/Cu FGM under transient thermal load of electron beam was performed. In the experiment, SEM and EDS analysis indicated that B4C and SiC were decomposed, carbon was preferentially evaporated under high thermal load, and a part of Si and Cu were melted, in addition, the splash of melted metal and the particle emission of brittle destruction were also found. Different erosive behaviors of carbon-based materials (CBMs) caused by laser and electron beam were also discussed.

Heat source analyses of dual laser-beam bilateral synchronous welding for T-joint

The DLBSW（ dual laser-beam bilateral synchronous welding） technology of T-type joint has been widely used for the connection of skins and stringers in airplane industry. To understand the thermodynamic and mechanical behavior of this process, it is necessary to establish a reasonable heat source model. Two different surface-body combination heat source models are adopted in this paper. Both models use the Gaussian surface heat source model and one is combined with the cone body heat source model and the other is combined with Gaussian rotator body heat source model. The simulation results of these two different models are investigated. And the temperature field results of DLBSW process for T-joint with two different heat sources are discussed. It is indicated that the combination heat source model is effective to simulate the DLBSW process and the current study is useful for more profound research in this field.