SLMed Alloy Research Articles

Insight into the hot corrosion behavior of GH4251 high-temperature superalloy fabricated by selective laser melting

In this study, the GH4251 high-temperature superalloy was fabricated using selective laser melting (SLM) and hot isostatic pressing (HIP) post-treatment. The hot corrosion behavior of the SLMed and SLM-HIPed GH4251 was systematically investigated and compared with the as-forged one in a mixed salt of 75 % Na2SO4 and 25 % NaCl at 900 °C. The results indicated that three GH4251 superalloys rank in order of superiority for high-temperature corrosion resistance as follows: SLMed > SLM-HIPed > as-forged. The hot corrosion resistance of the alloy is closely related to its microstructures. A high density and a high proportion of small-angle grain boundaries effectively prevent substrate corrosion from molten salts. High dislocation densities and fine grains can increase the elemental diffusion channels and promote the formation of dense protective oxide films, thereby enhancing the hot corrosion resistance. The SLMed superalloy has high densities, high dislocation densities, a high proportion of small-angle grain boundaries, and an appropriate grain size. This is the reason why the SLMed alloy exhibits the most superior hot corrosion resistance. In addition, the hot corrosion mechanisms of the GH4251 superalloy were also discussed in depth.

Forging Treatment Realized the Isotropic Microstructure and Properties of Selective Laser Melting GH3536

The anisotropy of mechanical properties in SLMed alloy is very important. In order to realize the homogeneity of the microstructure and mechanical properties of GH3536 alloy prepared by selective laser melting (SLM), the as-deposited samples were treated by hot isostatic pressing and then forged at different temperatures. The microstructure, grain size, room- and high- temperature tensile properties, and endurance properties of the samples were studied. The results showed that the microstructure of the sample was mainly equiaxed austenite phase, and granular carbides were precipitated inside the grains after forging treatment, resulting in the anisotropy of the sample almost disappearing. The grain boundary phase difference distribution was most concentrated at 60°. The grain size was less than 10 μm, and a large number of twins were formed. With the increase in forging temperature, the yield strength, tensile strength, and contraction of area of the samples changed little, and the properties parallel to the z-axis (parallel samples) and vertical to the z-axis (vertical samples) were almost the same. In particular, the yield strength, tensile strength, and contraction of area in the transverse and vertical samples were almost at the same level. Judging from the elongation after fracture and the contraction of area, the properties of the samples showed characteristics of anisotropy after a high temperature endurance test.

Microstructure evolution, martensite transformation and mechanical properties of heat treated Co-Cr-Mo-W alloys by selective laser melting

The influence of laser energy density and heat treatment on the microstructure and properties of Co-Cr-Mo-W alloys fabricated by selective laser melting (SLM) are investigated symmetrically. When the laser power, the scanning speed, and the scanning space are set as 160 W, 400 mm/s, and 0.07 mm, respectively, the SLM-ed Co-Cr-Mo-W alloys display high strength and good ductility simultaneously. The precipitates ranging from nano- to macro- scale are finely distributed in SLM-ed CoCr alloys grains and/or along the grain boundaries in the heat treated alloys. Co-Cr-Mo-W alloys with an excellent combination of strength and ductility can be achieved by tailoring the microstructure and morphology of SLM-ed alloys during the heat treatment. The tensile strength, yield strength, and elongation are 1221.38 ± 10 MPa, 778.81 ± 12 MPa, and 17.2 ± 0.67%, respectively.

Development of an accurate “composition-process-properties” dataset for SLMed Al-Si-(Mg) alloys and its application in alloy design

Al-Si-Mg series alloys are the most common alloys available for additive manufacturing forming with low cracking tendency. However, there is no systematic study on the computational design of SLMed Al-Si-(Mg) alloys due to the huge parameter space of composition and processes. In this paper, a high-quality dataset of SLMed Al-Si-(Mg) alloys containing 176 pieces of data from 50 publications was first established, which recorded the information, including alloy compositions, process parameters, test conditions, and mechanical properties. A threshold value of 35 J/mm3 for energy density (Ed) was then proposed as a criterion to clean the data points with lower ultimate tensile strength (UTS) and elongation (EL). The cleaned dataset consists of a first training/testing dataset with 142 data for model construction and a second testing dataset with 9 data for model verification. After that, four machine learning models were applied to establish the quantitative relation of “composition-processes-properties” in SLMed Al-Si-(Mg) alloys. The MLPReg model was chosen as the optimal one considering its best performance and subsequently utilized to design novel compositions and process parameters for SLMed Al-Si-(Mg) alloys. The UTS and EL of the designed alloy with a maximum comprehensive mechanical property are 549 MPa and 16%, both of which are higher than all the available experimental data. It is anticipated that the present design strategy based on the machine learning method should generally be applicable to other SLMed alloy systems.

Corrosion Resistance of Selective Laser Melted Ti6Al4V3Cu Alloy Produced Using Pre-Alloyed and Mixed Powder.

Metallic elemental powder mixture and pre-alloyed metallic powder are both frequently used powder feedstock in the additive manufacturing process. However, little research has been conducted to compare the corrosion behavior of selective laser melting (SLM) alloys, fabricated by pre-alloyed metallic powder and mixed metallic powder. Hence, it is important to investigate the corrosion behavior of SLMed alloys, as well as the corresponding cast ingot, with the aim to better understand the feasibility of designing new materials. In this work, the SLM-produced Ti6Al4V3Cu alloys were manufactured using a metallic elemental powder mixture and pre-alloyed metallic powder, respectively. The corrosion behavior of the different Ti6Al4V3Cu alloys was investigated in following electrochemical tests and ion release measurements. The results showed that the Ti6Al4V3Cu alloy prepared by pre-alloyed metallic powder showed better corrosion resistance than that produced from mixed metallic powder. Moreover, the SLM-produced Ti6Al4V3Cu alloys performed significantly better in corrosion resistance than the cast Ti6Al4V3Cu. The results are expected to achieve a better understanding of the feasibility of designing new materials using mixed powders, contributing to reducing development costs and cycles.

Effects of post-production heat treatment on the mechanical and corrosion behaviour of CoCrMoW alloy manufactured through selective laser melting

In this work, the matrix of CoCrMoW alloy fabricated by selective laser melting is mainly γ-Co phase. After the aging treatment at 750 °C, lamellar ε-Co phase formed according to a Shoji-Nishiyama orientation relationship with γ-Co phase and nanometer-scaled Co3(Mo,W)2Si precipitation uniformly distributed on the matrix, the strength and corrosion resistance increased, but the ductility decreased. After the solution treatment at 1200 °C, recrystallization happened, the fine columnar sub-grains of γ-Co phase in the as SLMed alloy were replaced by larger grains mainly with large-angle grain boundaries, the ductility increased, but the tensile strength and corrosion resistance decreased. Results of this work can provide a perspective towards microstructure regulation of SLMed CoCrMoW alloy.

Effect of heat treatment on microstructure evolution and mechanical properties of selective laser melted Mg-11Gd-2Zn-0.4Zr alloy

The Mg-11Gd-2Zn-0.4Zr (GZ112K, wt.%) alloys fabricated by selective laser melting (SLM) still contain some hard and brittle β-(Mg,Zn)3Gd eutectic phase with an area fraction of 4.86% despite the ultra-fast cooling rate of SLM process, so post heat treatment is necessary. The effects of different solution conditions and aging heat treatment on microstructure and mechanical properties of the SLMed GZ112K alloys were systematically analyzed. The results show that the optimized solution condition (400 °C × 12 h) for the SLMed GZ112K alloys can not only transform hard and brittle β-(Mg,Zn)3Gd eutectic phase into relatively softer lamellar 14H type long period stacking order (LPSO) structure leading to the improved elongation (EL) of the SLM-T4 alloys, but also retain the fine grains of the SLMed GZ112K alloys to a large extent with a small average grain size of 3.1 μm in the SLM-T4 state contributing to the high yield strength (YS) of the SLM-T4 and SLM-T6 GZ112K alloys. After peak aging heat treatment, basal γ′ precipitates or lamellar 14H-LPSO structure and dense prismatic elliptical β′ precipitates coexist in the SLM-T6 GZ112K alloys. As a result, the SLM-T6 GZ112K alloys exhibit YS of 343 ± 9 MPa, ultimate tensile strength (UTS) of 371 ± 4 MPa and EL of 4.0 ± 0.05%, while those of the SLMed GZ112K alloys are 332 ± 3 MPa, 351 ± 5 MPa and 8.6 ± 1.0%. The ultra-high YS of SLM-T6 GZ112K alloys results from the fine grain strengthening, the precipitation strengthening from β′ aging precipitates, the secondary phase strengthening from LPSO structure and X phase and the extra composite strengthening from the coexistence of basal and prismatic precipitates. The findings indicate that appropriate post heat treatment is an effective scheme for modifying microstructure and mechanical properties of the SLMed alloys.

Microstructure and mechanical properties of Al-Fe-Sc-Zr alloy additively manufactured by selective laser melting

An Al-5Fe-1Mg-0.8Sc-0.7Zr (wt%) alloy was specifically designed for selective laser melting (SLM) additive manufacturing and atomized powder prepared. The design of this non-equilibrium alloy is based on: first, solid solubility of Fe element in Al alloy can be significantly enlarged during laser rapid solidification; second, Sc and Zr elements are used to refine the microstructure so as to prevent micro-crack and improve strength. At an optimized printing parameters, the SLM printed Al-Fe-Sc-Zr samples exhibited a highest density of 99.2% with rare intergranular cracks. Besides, a bimodal grain structure was observed, consisting of ultrafine equiaxed grain at molten pool boundary and coarse columnar grain inside the molten pool. At the boundary of molten pool, many intermetallic particles (Al 6 Fe and Al 13 Fe 4 ) appeared around supersaturated α-Al grains; while the inside of molten pool presented eutectic of α-Al and Al 6 Fe/Al 3 (Sc, Zr). Interestingly, a large number of stacking faults were observed around the precipitated particles by HRTEM, which are also conducive to strengthening of SLM printed Al-Fe-Sc-Zr sample. Thus, excellent tensile strength of 489 MPa was obtained at an optimized volumetric energy density (VED) of 70 J/mm 3 . The current research results have a certain guiding significance for the composition design and microstructure control of additive manufacturing aluminum alloys. • High Fe-content Al-Fe-Sc-Zr alloy was successfully printed by selective laser melting. • The microstructure is composed of supersaturated solid solution and fine precipitates. • An eutectic microstructure of α-Al and Al 6 Fe/Al3(Sc, Zr) phases was found. • YS and UTS of SLMed alloy reached 388 ± 14 MPa and 489 ± 6 MPa, respectively.

Design, microstructure and thermal stability of a novel heat-resistant Al-Fe-Ni alloy manufactured by selective laser melting

Selective laser melting (SLM) technology is promising to fabricate complex-shaped metal components, especially light-weight aluminum (Al) alloy. Facing the grow requirement of thermal stability for applications in aviation and aerospace at high temperatures, the poor thermal stability of Al alloy needs to be improved. Thus, in this study, we developed a novel heat-resistant eutectic Al-Fe-Ni alloy which is suitable for the SLM process. Firstly, the composition of Al-1.75Fe-1.25Ni (wt%) alloy was designed and confirmed through the calculation of hot crack susceptibility index |dT/d(fs0.5)| and the analysis of the as-cast microstructure. Then, the designed alloy was fabricated using the optimized SLM processing parameters. Finally, the effects of heat treatment on microstructure evolution and phase stability during thermal exposure were investigated. Results show that the SLMed alloy is consisted of α-Al and cellular eutectic Al9FeNi phases. The fine grain structure and nano-sized Al9FeNi phase of the SLMed sample result in high hardness which is more than twice higher than that of the as-cast sample. During long-term thermal exposure at 300 °C, the fine grain structure and cellular eutectic phase remain almost unchanged, and thus, the hardness of the alloy can be kept stable. When the exposure temperature further increased, the fine grains gradually grew up and the cellular Al9FeNi phases were gradually collapsed and coarsened. Heat treatment at such high temperature (above 400 °C) resulted in microstructure coarsening and formation of large-sized rod-like or spherical phases, which significantly degraded the hardness. The novel heat-resistant Al-Fe-Ni alloy together with the alloy composition design method provides new insight into light-weight and complex-shaped components produced by the SLM process for high-temperature applications.

Influence of friction stir processing and aging heat treatment on microstructure and mechanical properties of selective laser melted Mg-Gd-Zr alloy

The low ductility of Mg alloy fabricated by selective laser melting (SLM) technique usually restricts its application in several fields. Friction stir processing (FSP) is a promising post-treatment method to solve this problem. A detailed study of how FSP affect pore defects, molten pool boundary, grain morphology, aging precipitates and mechanical properties of SLMed Mg-10Gd-0.2Zr (G10K, wt.%) alloy was conducted. The results show that FSP can lead to porosity reduction from 0.779% to 0.015%, vanishment of molten pool boundary, columnar to equiaxed transition and grain refinement. Thus, a significant enhancement of room temperature tensile properties is reported with a remarkable increase of elongation (EL) from 2.2% to 7.5% without the sacrifice of strength after FSP (while yield strength (YS) and ultimate tensile strength (UTS) increased from 180 MPa, 228 MPa to 202 MPa, 272 MPa respectively). After peak aging heat treatment, the plate aspect ratio and area number density of β' aging precipitates in the FSP-T5 G10K alloy are higher than those of SLM-T5 G10K alloy, resulting in a stronger aging hardening response (hardness increment 28.3 HV versus 22.7 HV). As a result, the FSP-T5 G10K alloy exhibits YS of 285 MPa, UTS of 356 MPa and EL of 1.3%, while those of the SLM-T5 G10K alloy are only 243 MPa, 260 MPa and 0.3%. These findings demonstrate that FSP is very effective for modifying microstructure and enhancing mechanical properties of the SLMed alloys.

Additive manufacturing of a quasicrystal-forming Al95Fe2Cr2Ti1 alloy with remarkable high-temperature strength and ductility

Abstract This work investigated the phase formation, thermal stability, and mechanical behavior of a metastable quasicrystal-forming Al95Fe2Cr2Ti1 alloy prepared by selective laser melting (SLM). The powder of this alloy was obtained by gas atomization using recycled material (Al cans) which brings several economic and social advantages. It showed chemical composition, particle size distribution, flowability, and morphology adequate for the SLM process. Samples were produced by SLM in different build directions (0°, 45°, and 90°) with a high relative density of 99.3–99.8%. SLM processing of quasicrystal-forming Al95Fe2Cr2Ti1 powder led to the formation of a microstructure including the presence of nm-sized quasicrystalline precipitates in a dendritic α-Al matrix mainly in the center of the molten pool while the heat-affected zones showed coarser but also nanometric quasicrystalline and crystalline phases. Similar phase formation and hardness of 180.33 HV were observed at the top and bottom of the samples, independent of the build direction. Due to the formation of ultrafine precipitates and refined grains the samples exhibited a high compressive strength at room temperature and 400 °C. The material exhibited a remarkable 140 ± 13 MPa yield strength along with extensive compression ductility at 400 °C, which is higher than what is observed for AlSi SLMed alloys and conventionally processed high-temperature Al alloys. These results show a new opportunity to fabricate higher-performance high-temperature quasicrystal-forming alloys with freedom of geometry design and lower cost.

Microstructure and magnetic properties of FeSiBCrC soft magnetic alloy manufactured by selective laser melting

To investigate the microstructure and magnetic properties, FeSiBCrC bulk soft magnetic alloy was prepared by selective laser melting (SLM) technology using amorphous feedstock powder in this work. The results show that amorphous structures and crystalline phases occur in the alloy. And this alloy is mainly composed of α-Fe(Si), Fe3Si, FeB and Fe2B. It is mainly composed of metastable grains, equiaxed grains and amorphous matrix. This alloy has high microhardness (nearly 900 HV0.1). The SLMed alloy exhibits good soft magnetic properties. The coercivity of the direction X and direction Z is almost the same, which is 78.8 Oe. And it has great saturation magnetization with 162 emu/g in both directions. This work reveals the potential of fabricating bulk Fe-Si based amorphous soft magnetic alloys via SLM.

Multi-scale microstructure high-strength titanium alloy lattice structure manufactured via selective laser melting.

The tensile performance of Ti6Al4V alloy lattice structure was investigated. Firstly, a face center cubic unit cell with vertical struts (F2CCZ) lattice structure was designed. Then, the structures were fabricated by selective laser melting (SLM) with different aspect ratios. Subsequently, the SLM-ed alloys were subjected to double solution-aging to homogenize the microstructure and release residual stress. It is shown that there is only acicular α′ martensite with high dislocation density in the SLM-ed alloy, while the heat-treated alloy has α and β phases (there are multi-scale α laths and nano-scale β particles), and the orientation relationship between the two phases is: [113]β//[1210]α. The tensile strength of the HT-ed alloys presents a significant increase from 140 ± 18 MPa in the SLM-ed state to 229 ± 5.1 MPa with an aspect ratio of 4. It indicates that the special heat treatment regime can not only homogenize the microstructure of the SLM-ed alloy, but also improve the tensile strength.

Inoculation treatment of an additively manufactured 2024 aluminium alloy with titanium nanoparticles

Considerable studies on metal selective laser melting (SLM) have proved the necessity to refine microstructure parts fabricated by SLM in order to eliminate property anisotropy, hot-tearing and to increase the SLM-processability. In the present work, Ti nanoparticles, at the first time, were discovered to be an extremely effective inoculant for an SLMed 2024 aluminium alloy. 0.7 wt% addition of Ti nanoparticles was capable of substantially eliminating the hot-tearing cracks and columnar structure, and refining the grains in the SLMed 2024 alloy in a broad processing window. The substantial grain refinement in the Ti-inoculated 2024 alloy was attributed to the in-situ formation of Al3Ti nanoparticles with a L12 ordered structure, which formed a coherent interface with Al matrix and therefore significantly promoted the heterogeneous nucleation of the α-Al during solidification of melt pools in the SLM process. After a conventional T6 heat treatment, this SLMed alloy exhibited a superior balance of strength and ductility (tensile strength was up to 432 ± 20 MPa and elongation of 10 ± 0.8%), which was comparable to its wrought counterpart. This work can be considered as a breakthrough in research of fabricating high-strength aluminium alloys using SLM.

Heat treatments design for superior high-temperature tensile properties of Alloy 625 produced by selective laser melting

The popular superalloy Alloy 625 was produced by Selective Laser Melting (SLM) and post-processing heat treatments were designed to optimize the inhomogeneous and constrained as-built microstructure (AB) for high temperature structural applications. A single-step solution heat treatment (RX) was designed to promote full recrystallization and approach the conventional wrought microstructure. To enhance high temperature properties, a grain boundary serration heat treatment (GBS) was successfully designed involving higher solution temperature and time to promote recrystallization and homogeneity, and a direct slow cooling step followed by a short aging to assist solute diffusion and grain boundary motion. The resulting microstructures were characterized by fully recrystallized fine equiaxed grains and fine intra and intergranular NbC precipitates. The GBS alloy also exhibited as much as 80% of serrated grain boundaries with enhanced resistance to cracking at high temperatures. Tensile properties of all three materials were evaluated at room temperature, 500 °C, 600 °C and 700 °C and compared with their conventional solutionized wrought Alloy 625 counterpart (Wrought). While the AB material exhibited high strength and low ductility, due for the most part to the high density of tangled dislocations resulting from SLM, both RX and GBS alloys showed tensile properties comparable to the conventional wrought material, higher strength in particular. At all temperatures, all four alloys exhibited yield strength values well over 200 MPa. Due to significantly different microstructures, deformation and fracture behaviors were different. While Wrought clearly presented irregular plastic flow at elevated temperatures typically attributed to dynamic strain aging (DSA), the materials produced by SLM and moreover those subjected to post-processing heat treatments exhibited more stable plastic deformation. The results and characterization reported in the present article highlight the predominant role of microstructure and outstanding potential of SLMed Alloy 625.

Inoculation Treatment of an Additively Manufactured 2024 Aluminium Alloy with Titanium Nanoparticles

Considerable studies on metal selective laser melting (SLM) have proved the necessity to refine microstructure parts fabricated by SLM in order to eliminate property anisotropy, hot-tearing and to increase the SLM-processability. In the present work, Ti nanoparticles, at the first time, were discovered to be an extremely effective inoculant for an SLMed 2024 aluminium alloy. 0.7 wt.% addition of Ti nanoparticles was capable of substantially eliminating the hot-tearing cracks and columnar structure, and refining the grains in the SLMed 2024 alloy in a broad processing window. The substantial grain refinement in the Ti-inoculated 2024 alloy was attributed to the in-situ formation of Al3Ti nanoparticles with a L12 ordered structure, which formed a coherent interface with Al matrix and therefore significantly promoted the heterogeneous nucleation of the α-Al during solidification of melt pools in the SLM process. After a conventional T6 heat treatment, this SLMed alloy exhibited a superior balance of strength and ductility (tensile strength was up to 432 ± 20 MPa and elongation of 10 ± 0.8%), which was comparable to its wrought counterpart. This work can be considered as a breakthrough in research of fabricating high-strength aluminium alloys using SLM.

Investigation into the dynamic mechanical properties of selective laser melted Ti-6Al-4V alloy at high strain rate tensile loading

In general, mechanical properties of most materials under dynamic loading are completely different from those under static/quasi-static loading. In this paper, a comparative study between the selective laser melted Ti-6Al-4V alloy and its heat-treated counterpart was carried out. After heat treatment, the microstructure transformed from full fine acicular α' into basket-weave morphology with coarsened α + β lamella, grain boundaries α tended to globularization, and the volume fractions of β phase and LAGBs increased due to the α′→α + β transformation and increasing of dislocation density respectively. During high strain rate tension, strain was dispersive in the elastic deformation region, then it began to concentrate at the centre of samples and increased until fractured as loading time increased. As expected, evident reduction in the UTS and σy and increase in the ε were caused by heat treatment, however both of them increased as the strain rate increased due to the twinning deformation occurred in the α/β interface phase, thus contributed to improving the strength and plasticity of SLMed TC4 alloy under high strain rate loading simultaneously. This work provided a relationship between microstructure and dynamic responses of SLMed TC4 alloy, which contributes to exploiting the performance potential of SLMed alloy.

Grain boundary network evolution in Inconel 718 from selective laser melting to heat treatment

Inconel 718 fabricated by selective laser melting (SLM) was used to investigate the evolution of grain boundary (GB) network structures from as-SLM to heat-treated (HT) samples. Using electron backscatter diffraction (EBSD) data and percolation theory based cluster analysis, GB character distribution and GB network topological metrics were computed at different build locations and directions. The microstructures of the as-SLM samples reveal large spatial heterogeneity in grain morphology and are dominated by general GBs (i.e., ∑> 29), which form one connected cluster spanning across the whole GB network. Heat-treatment homogenizes the microstructure and leads to the formation of annealing twins as a result of recrystallization, which dramatically increases the number of special boundaries (mainly twin ∑3 and twin-related ∑9, ∑27 boundaries with ~ 60% in boundary length fraction). However, these special boundaries have not yet fully connected/merged to form a percolated path throughout the GB network. The triple junction distributions of the HT sample are dominated by J1-type that consists of one special and two general boundaries, further confirming the interweaving GB network made of the general and special boundary clusters. In addition, the implication of applying GB engineering to the SLMed parts is discussed based on the comparison of GB network structures between the SLMed alloys and the conventionally GB engineered metals and alloys.

Prediction of microstructure in selective laser melted Ti[sbnd]6Al[sbnd]4V alloy by cellular automaton

Selective laser melting (SLM), as a powder-bed-based additive manufacturing technology, is a promising technology for manufacturing metal parts with high geometric complexity. The prediction of the SLMed microstructure, a key approach to manipulate the microstructures and performances, is challenging due to the complex heat history involving multiple thermal cycles. In the work, the microstructural simulation of solidification and solid-state phase transformation processes under various spatially variable thermal cycles of SLM was investigated by a developed two-dimensional cellular automaton (CA) model considering the temperature distribution and transient thermal history. The morphology and size of the β grain and martensite simulated by the model agree well with the experimental results in single-layer, thin-wall and multi-track multi-layer samples. Based on the simulated results, there are three zones (powder melting, remelting and reheating zones) and four stages (powder melting, mushy, multi-phases and solid-state phase transformation stages) during SLM depositing Ti6Al4V alloy. The morphology, growth direction and size of prior β grains depend mainly on the direction of heat flux and overlapping of adjacent deposited tracks. Six evolutional types of β grains exist including disappearance, morphological change, size increasing to be a stable value, growing, size decreases to be a stable value, and no evolution. The prediction of microstructure in SLMed alloy can be realized by the developed CA model.

Crystallographic features of α variants and β phase for Ti-6Al-4V alloy fabricated by selective laser melting

The present study investigated the crystallographic features of α variants and β phase for Ti-6Al-4V alloy fabricated by selective laser melting. The <100>β fiber texture parallel to the building direction was ascertained on the basis of a reconstruction method realized by the manipulation of stereographic projection. The SLMed alloy has no α/α′ variants selection but contains a special crystallographic area exhibiting random orientation which cannot be reconstructed as a parental columnar β grain with the present introduced method due to its nature as the overlapped area between adjacent melt pools resulting from the heterogeneous nucleation in front of the liquid-solid interface. With increasing the heat treated temperature, α variants selection occurs. Especially at higher temperature of 905°C, the intergranular β phase following a reversed crystallographic path as “parental β phase”→“α variants”→“intergranular β phase” would be precipitated, therefore the intergranular β phase keeps the same orientation with the parental β phase. Once the alloy was heat treated at 975°C close to Tβ, the microstructure is characterized by primary α variants selection and a large amount of secondary α widmanstatten structure with a homogeneous orientation which accounts for the lowest tensile strength. The decomposition of twelve α variants proved the BOR <110>β//(0001)α, <111>β//<2-1-10>α. The misorientation between two variants sharing a common parental <100>β pole with a similar color consisting of all Euler angles was identified to be [0001] α/10.53°.