Laser Melting Deposition Research Articles

Mechanical and electrochemical corrosion properties of titanium by laser melting deposition

Mechanical and electrochemical corrosion properties of titanium by laser melting deposition

Graded microstructure and properties of TiCp/Ti6Al4V composites manufactured by laser melting deposition

In this paper, 50 vol% TiCp/Ti6Al4V composites without pores, cracks or poor fusion were fabricated by laser melting deposition (LMD) technology using 500 W laser power (lower power, LP) and 1000 W laser power (higher power, HP). The microstructure of different deposited layers was analyzed and the corresponding microhardness was measured. The results show that the composites are composed of undissolved TiC, in-situ TiC (eutectic TiC and primary TiC), α Ti and β Ti. It is interesting that the microstructure from the bottom layer to the top layer presents a graded distribution when all layers have the same composition. The eutectic TiC is mainly formed in lower layers while the primary TiC is mainly in upper layers. With increasing layer number, the size and number of the primary TiC grains increase and the primary TiC grows gradually from granules into dendrites, however, the number of the undissolved TiC particles decreases along the depositing direction. The simulation results show that the peak temperature of deposited layer increases while the cooling rate decreases with increasing layer number. Different thermal history affects the diffusion of carbon and the evolution of TiC, and then affects the microstructure distribution of the composites. This graded microstructure leads to the graded distribution of microhardness. The microhardness of the LP composite rises from 432.5 HV to 488.1 HV, while the HP composite rises from 435.5 HV to 604.3 HV from the bottom layer to the top layer, respectively.

Cu-bearing 316L stainless steel coatings produced by laser melting deposition: Microstructure and corrosion behavior in simulated body fluids

In order to clarify the effect of copper contents on the corrosion resistance of stainless steel in biological environment, 316L-0Cu (wt%), 316L-1.5Cu (wt%), 316L-4.5Cu (wt%) and 316L-7.5Cu (wt%) coatings were prepared by laser melting deposition (LMD), and the microstructure and corrosion behavior in simulated body fluids (SBF) were studied. The results show that the planar growth, cellular crystal and dendritic microstructure are formed in the four kinds of LMD-produced coatings. With the increase of copper contents, the microstructure is refined, the corrosion resistance is decreased first and then is increased. This is because the copper oxide precipitates at the high-density grain boundaries, which can promote the passivation behavior. Under the combined action of Cr2O3 and Cu2O, the corrosion resistance of 316L-7.5Cu coating is closest to that of 316L-0Cu coating.

Microstructural evolution along the build height of laser melting deposited TA15 alloy

This study emphasizes the TA15 alloy microstructural distribution fabricated by the laser melting deposition (LMD) technique. The motivation of the study is to analyze the microstructural features, such as grain or laths thickness, phase fraction, and porosity occurrence in the different regions along the build height, due to the complex thermal-solidification history during the laser melting deposition. During laser deposition of titanium alloy, the laser beam forms a melt pool, where the near-α and α+β alloys transform into a single β-phase, followed by rapid solidification. This process is repeated when a successive layer is deposited, where the previously deposited layers are re-melted. These thermal cycles can affect the parent microstructure in the previously deposited layers. It was identified from the results that the width of α-laths was larger in the regions near the top of the build component. In comparison, the bottom region near to substrate contained fine laths due to a steep thermal gradient and repeated thermal effect. The volume fraction of β-phase was higher in the bottom region, which could be regarded as the transformed β matrix due to the successive thermal effect in the α+β field. The results also showed shallow porosity existence in the top and near to top regions. According to the morphology and size, the formation of these pores can be attributed to the gas entrapment during the deposition process.

Effect of Powder Feeding Rate on the Forming Quality of Alloy by Laser Melting Deposition

12CrNi2 alloy steel was prepared by Laser Melting Deposition (LMD) technology, and the effect of powder feeding rate on surface quality, internal defects, microstructure, and microhardness of the single track and manufactured part were investigated. The results show that the metallurgical bonding of the single track deteriorates, the surface quality of the manufactured part is improved, the average microhardness of the manufactured part increases, and the number of pores first decreases and then increases with the increase of powder feeding rate. At the lower powder feeding rate, the manufactured parts have larger pore defects, while at the higher powder feeding rate, the manufactured parts have poor fusion defects. The main phase composition of the manufactured parts is ferrite(F), granular bainite (GB), and pearlite(P), and the manufactured part has finer grains at the higher powder feeding rate.

Fabrication of laminated high entropy alloys using differences in laser melting deposition characteristics of FeCoCrNi and FeCoCrNiAl

Here, in order to develop the metallic materials with excellent relationship between strength and toughness for application, the FeCoCrNi + FeCoCrNiAl-laminated high-entropy alloys (HEAs) had been fabricated by laser melting deposition (LMD) additive manufacturing technique. The process parameter databases for FeCoCrNi and FeCoCrNiAl HEAs were built by orthogonal experiments and statistics method, which helped to select the optimised process parameters for the two HEAs. Then, the differences in the forming process, phase structure, and grain morphology of FeCoCrNi and FeCoCrNiAl HEAs were systematically investigated during the fabrication of the FeCoCrNi + FeCoCrNiAl-laminated HEAs. The results show that variations in surface tension, wettability, and other physical properties between the two HEAs led to significant differences in their LMD processes. Al not only influenced the fabrication process of both HEAs, but also promoted the phase transition from FCC (FeCoCrNi) to BCC (FeCoCrNiAl). In addition, Al also acted as a strong limiting factor to inhibit the effect of supercooling on the grain morphology, which transformed from coarse columnar grains to fine equiaxed grains. The columnar grains, with a preferred orientation in the FeCoCrNi-deposited wall, promoted the suppression of the inhibitive effects of the phase structure and strong limiting factor, led to the growth of the columnar grains in the FeCoCrNiAl-deposited wall, and helped achieve long-distance continuous growth of columnar grains across the interface in the subsequently deposited wall. The methodology used in this study could be meaningful for the exploration of process parameters of LMD, and the discoveries of grain characteristic help to understand the microstructure transition in laminated heterogeneous HEAs fabricated by laser additive manufacturing.

Strength and ductility optimization of laser additive manufactured metastable β titanium alloy by tuning α phase by post heat treatment

The metastable β titanium alloy Ti–5Mo–5V–8Cr–3Al (TB2) was fabricated by laser melting deposition (LMD). α phase was tuned by post heat treatment (PHT) in order to obtain a good combination of strength and ductility of laser melting deposited (LMDed) TB2 alloy. This study demonstrated that TB2 alloy exhibited fully equiaxed β phase after LMD, which possessed good ductility (≈18.2%) with ultimate tensile strength (σUTS) of 811 MPa. The β solution plus aging treatments resulted in higher strength (σUTS ≈ 1136–1312 MPa) in comparison with the (α+β) solution plus aging treatments (σUTS ≈ 1037 MPa) because of higher-density acicular α phase with finer size (width∼200 nm). Two-step aging resulted in improved ductility (≈9.8–12.9%) in comparison with the one-step aging (≈2.0%) due to coarsening of α phase. Finally, β solution plus two-step aging was proved to be appropriate for LMDed TB2 alloy to achieve a good combination of strength (σUTS ≈ 1136 MPa) and ductility (≈9.8%).

A state-of-the-art review of the fabrication and characteristics of titanium and its alloys for biomedical applications.

Commercially pure titanium and titanium alloys have been among the most commonly used materials for biomedical applications since the 1950s. Due to the excellent mechanical tribological properties, corrosion resistance, biocompatibility, and antibacterial properties of titanium, it is getting much attention as a biomaterial for implants. Furthermore, titanium promotes osseointegration without any additional adhesives by physically bonding with the living bone at the implant site. These properties are crucial for producing high-strength metallic alloys for biomedical applications. Titanium alloys are manufactured into the three types of α, β, and α + β. The scientific and clinical understanding of titanium and its potential applications, especially in the biomedical field, are still in the early stages. This review aims to establish a credible platform for the current and future roles of titanium in biomedicine. We first explore the developmental history of titanium. Then, we review the recent advancement of the utility of titanium in diverse biomedical areas, its functional properties, mechanisms of biocompatibility, host tissue responses, and various relevant antimicrobial strategies. Future research will be directed toward advanced manufacturing technologies, such as powder-based additive manufacturing, electron beam melting and laser melting deposition, as well as analyzing the effects of alloying elements on the biocompatibility, corrosion resistance, and mechanical properties of titanium. Moreover, the role of titania nanotubes in regenerative medicine and nanomedicine applications, such as localized drug delivery system, immunomodulatory agents, antibacterial agents, and hemocompatibility, is investigated, and the paper concludes with the future outlook of titanium alloys as biomaterials.Graphic abstract

Effect of discrete deposition and segregated heat-treatment on the macro- and microstructure, and tensile properties of large-scale titanium alloy components by laser melting deposition

The challenge of fabrication large-scale laser melting deposited titanium alloy (LLMDT) components was high residual stress, warpage deformation, and even fracture during long-time continuous deposition. To address this challenge, a method named discrete deposition and segregated heat-treatment (DDSH) was used to fabricate the LLMDT components and its effect on the macro- and microstructure, and tensile properties have been systematically studied. The results showed the macrostructure of the DDSH interface region showed columnar grains due to its higher thermal gradient and lower solidification rate than them in other LLMDT parts with columnar grains and equiaxed grains. The microstructure in the whole LLMDT components consisted of ultrafine basket-weave microstructure. The average width of the α lamellae in the DDSH interface region and other LLMDT parts was 0.38–0.424 μm and 0.477–0.54 μm, respectively. The average width of α lamellae was finer in the DDSH interface region than that in the other LLMDT parts owing to its higher thermal gradient and higher cooling rate compared with the other LLMDT parts. For the LLMDT components in different directions with the same region, the UTS and the YS in the H-sample were slightly higher than those in the V-sample, while the EL in the H-sample was lower than those in the V-sample. The anisotropic ductility was owing to the continuous grain boundary exhibited different fracture mechanisms under different directions with loading stress. For the LLMD components in different regions with the same direction, the highest fluctuation ratio of the UTS, the highest fluctuation ratio of the YS, and the highest fluctuation ratio of the EL was 0.012%, 0.08%, and 0.145%, respectively. The reason was the average with of the α lamellae in the whole LLMDT components showed a little difference.

Mesoscopic Computational Fluid Dynamics Modelling for the Laser-Melting Deposition of AISI 304 Stainless Steel Single Tracks with Experimental Correlation: A Novel Study

For laser-melting deposition (LMD), a computational fluid dynamics (CFD) model was developed using the volume of fluid and discrete element modeling techniques. A method was developed to track the flow behavior, flow pattern, and driving forces of liquid flow. The developed model was compared with experimental results in the case of AISI 304 stainless steel single-track depositions on AISI 304 stainless steel substrate. A close correlation was found between experiments and modeling, with a deviation of 1–3%. It was found that the LMD involves the simultaneous addition of powder particles that absorb a significant amount of laser energy to transform their phase from solid to liquid, resulting in conduction-mode melt flow. The bubbles within the melt pool float at a specific velocity and escape from the melt pool throughout the deposition process. The pores are generated if the solid front hits the bubble before escaping the melt pool. Based on the simulations, it was discovered that the deposited layer’s counters took the longest time to solidify compared to the overall deposition. The bubbles strived to leave through the contours in an excess quantity, but became stuck during solidification, resulting in a large degree of porosity near the contours. The stream traces showed that the melt flow adopted a clockwise vortex in front of the laser beam and an anti-clockwise vortex behind the laser beam. The difference in the surface tension between the two ends of the melt pool induces “thermocapillary or Benard–Marangoni convection” force, which is insignificant compared to the selective laser melting process. After layer deposition, the melt region, mushy zone, and solidified region were identified. When the laser beam irradiates the substrate and powder particles are added simultaneously, the melt adopts a backwards flow due to the recoil pressure and thermocapillary or Benard–Marangoni convection effect, resulting in a negative mass flow rate. This study provides an in-depth understanding of melt pool dynamics and flow pattern in the case of LMD additive manufacturing technique.

Thermal behavior and microstructure evolution mechanism of Ti6Al4V 80 mm thick plates jointed by laser melting deposition

The traditional welding processes are challenging to obtain an excellent jointed structure with a thickness of over 80 mm. Meanwhile, cyclic heating for large-scale manufacturing components worsens microstructure and mechanical properties after welding. Laser Melting Deposition (LMD) technology is put forward to break through the limit of large-scale jointing components widely used for manufacturing aerospace products. Therefore, the LMD experiment with coaxial powder feeding for joining a pair of X-groove Ti-6Al-4V thick plates (80 mm) with different thermal behaviors (including laser scanning speeds and cooling rates) is carried out in this paper. The morphology evolution of its microstructure at the equiaxed grain zone (EQZ) and the deposition area under different thermal behaviors are systematically investigated. Meanwhile, the relationship between microstructure evolution mechanism and tensile properties is further explored. The volume fraction and size of acicular α/α' phases at the EQZ or the deposition area keep a stable rising when the laser scanning speed increase from 10mm/s to 20mm/s. The α-Ti cluster phases are usually precipitate around the β grain boundary with a low scanning speed and cooling rate. By contrast, the orthogonal acicular martensitic α/α' phase can precipitate inside the β grain, forming a Basketweave structure with a high scanning speed and cooling rate. The Basketweave structure forming in β grains can coordinate the deformation and reduce the stacking effect of dislocations, which is beneficial for improving ductility. However, the α-Ti cluster phases precipitating around the β grain boundary usually cause local stress concentration at these locations, forming microcracks at this location and deteriorating the tensile properties.

Strengthening mechanism of Y2O3 nanoparticles on microstructure and mechanical properties of the laser additive manufacturing joint for large thickness TC4 titanium alloy

The laser additive manufacturing technology with laser melting deposition as the core technology presents superior efficient connectivity of titanium alloy components with large thickness and complex structure in the aerospace field. The content of nanoparticles affects the microstructure and properties of TC4 large thickness titanium alloy joint when it is manufactured with laser additive manufacturing. A pair of TC4 titanium alloy test plates with a thickness of 80 mm were connected by laser additive manufacturing technology with the mixed powder as filler material which was produced by adding different content Y2O3 nanoparticles into TC4 powder. Optical microscopy, scanning electron microscopy, micro-hardness test and tensile test were conducted to study the effect of Y2O3 content on the microstructure and mechanical properties of the TC4 titanium alloy joint. The strengthening mechanism and agglomeration weakening mechanism of Y2O3 nanoparticles on microstructure and mechanical properties was investigated based on the experimental results. It was found that the addition of more Y2O3 nanoparticles resulted in partial powder agglomeration and degradation of tensile strength. The results indicated that the columnar grains in the middle of the deposition zone with Y2O3 nanoparticles were finer than those without Y2O3 nanoparticles. The joint fracture mode gradually changed from plastic fracture to quasi-cleavage fracture with the increase of Y2O3 content. The average hardness values of the joint with various Y2O3 contents are all higher than that of the TC4 titanium alloy substrate.

Microstructures and mechanical properties of reduced activation ferritic/martensitic steel fabricated by laser melting deposition

Laser melting deposition (LMD) is a promising way for the fabrication of complex reduced activation ferritic/martensitic (RAFM) steel components which provides an exceptional opportunity to improve the existing designs and move toward fabricating fine features and complex geometries with higher efficiencies. It is well known that if steel members are welded together, defects will be concentrated in the welded joint. We can control the scanning path of the laser to achieve a complex component molding, avoiding welding. Considering the LMD technology, the results of each layer of powder molding will affect the fineness of the final processed products, such as laser power, scanning speed, defocus and so on, which are all important factors affecting the products. We control the size of powder particle size as a variable to conduct a study on RAFM steel supplemented by LMD technology for the first time, and its microstructure and grain size were analyzed. In terms of mechanical properties, its hardness, Charpy impact, tensile strength and elongation were measured. The results show that compared with other processing processes including Selective Laser Melting (SLM), rolling, welding joints, the tensile strength of RAFM steel manufactured by laser coaxial powder feeding is up to 1057.75 MPa, and there are no pores and almost no defects when using small particle size powder. The microstructure of LMD RAFM steel contains a large amount of lath martensite and δ-ferrite, and some precipitates such as Mx, whose average grain size decreases with the increase of powder particle size (5–150 μm). In this study, the laser additive process was monitored by high-speed photography, and the average grain size of LMD RAFM steel was further analyzed, and a reasonable explanation of its mechanical properties was given.

Microstructure and mechanical behavior of Cu–9Al–4Ni-3.5Fe-0.5Mn alloy fabricated by laser melting deposition

The Cu–9Al–4Ni-3.5Fe-0.5Mn Nickel-aluminum bronze (NAB) thin wall sample was prepared by laser melting deposition (LMD). The solidification characteristics, microstructure and mechanical properties were investigated. The LMD-NAB alloy consists of α, β′ and κ(κII, κIII, κIV) phase. The α phase shows directional growth trend along the deposition direction. Lamellar κIII phase distributed in α, and spherical shell κIII phase distributed on the surface of κIV phase were found. Spherical and parallelogram κIV phase was distributed in α phase. A core structure based on FeAl3 phase was located in the spherical and parallelogram κIV phase. The LMD-NAB alloy presents tensile properties with average ultimate tensile strength (UTS) of 645 ± 5.7 MPa and elongation of 21.2 ± 1.5% along the scanning direction, and tensile properties with average UTS of 637 ± 9.9 MPa and elongation of 26.0 ± 0% along the deposition direction. The fracture surfaces exhibit a mixture of brittle cleavage model and microvoid coalescence. This work shows great potential for fabricating NBA alloy by LMD technology.

Laser Melting Deposition of CP-Ti/Ti–0.4Ni Graded Material for Structural Applications

Laser Melting Deposition of CP-Ti/Ti–0.4Ni Graded Material for Structural Applications

Effect of heat accumulation on the microstructure of Invar alloy manufactured by multi-layer multi-pass laser melting deposition

Invar alloy has an important application in the manufacture of composite forming mould. The laser melting deposition (LMD) technology was utilized to fabricate multi-layer multi-pass deposited samples in this study. The effect of heat accumulation on the microstructure of deposition layer (DL) was investigated through experimental and simulation method. A finite element (FE) model was established to study the temperature field distribution in LMD process. Microstructure of DL was investigated by optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The thermal cycle curves were extracted for analysis. The accumulation of heat during the deposition process would make the higher location DL reach a higher peak temperature. It could be seen from the observation of the transverse section of the deposited samples that the microstructure consisted of elongated cellular crystals and regular cellular crystals. At the bottom of the DL were columnar crystals grown epitaxially along the maximum temperature gradient and gradually transitioned to equiaxed crystals at the top of the DL. EDS detection results showed that there was no element aggregation phenomenon in the DL. The grains in the remelted zone were coarsened due to suffering a state of overheating.

Circular oscillating laser melting deposition of nickel-based superalloy reinforced by WC: Microstructure, wear resistance and electrochemical properties

Circular oscillating laser was used to deposit GH3536 nickel-based superalloy, GH3536-16 wt.% coarse WC and GH3536-16 wt.% fine WC composite. The microstructure characteristics and evolution, phase composition and properties of the three materials fabricated by circular oscillating laser melting deposition were studied. In the mode of circular oscillating laser, equiaxed and columnar crystal structures are formed in the middle and edge of the cladding track of the three materials due to its temperature gradient distribution and the laser stirring effect on molten pool. The main phases of the composite coatings are γ-Ni solid solution, WC, W2C and M6C. WC particles uniformly distributed in GH3536 matrix have the effects of fine grain strengthening and dispersion strengthening. Compared with GH3536, the average microhardness of the composite material is increased by 59.70% (coarse WC) and 74.66% (fine WC) respectively, and the wear rate is reduced by 84.87% (coarse WC) and 89.17% (fine WC) respectively. The wear mechanism changes from adhesive wear to abrasive wear after adding WC. The corrosion current density of the composite coating is 44.9% (coarse WC) and 26.5% (fine WC) lower than that of GH3536, respectively. WC particles have physical shielding and solid solution strengthening effects, and improve the corrosion resistance of GH3536 coating.

Microstructure and properties of FeCoCrNi high entropy alloy produced by laser melting deposition

In this paper, the laser melting deposition (LMD) technology was applied to fabricate FeCoCrNi high entropy alloy (HEA), and the microstructure of the deposited HEA (FeCoCrNi-LMD) was systematically studied. The width of the columnar grains was found to increase gradually from the bottom to the top of the material. The top layer consisted of equiaxed grains. Tensile stress and compressive stress were applied to the material along and perpendicular to the direction of columnar grain growth, respectively. Electron Backscatter Diffraction (EBSD) and transmission electron microscopy (TEM) were used to observe the changes in the microstructure and properties of the material under the applied stresses. It was found that the phase structure of the material did not change when the stress was applied, but the maximum polar density increased. After stretching, the Schmid factor decreased, resulting in strain hardening. Dislocations moved during the plastic deformation and their number increased, resulting in many small angle grain boundaries and subgrain boundaries. The dislocations concentrated at the grain boundaries, leading stress concentration at the grain boundaries. In addition, due to the differences in the distribution of elements between the grains and the grain boundaries, the properties of grain boundaries changed. Cracks were produced easily along the grain boundaries during the tensile test. Under the compressive stress (rolling), for the same amount of rolling deformation, as the width of the columnar grains increased from the bottom to the top of the FeCoCrNi-LMD, the size of the columnar grains increased. As a result, the columnar grains were inclined at an angle to the rolling direction, and the rolled specimen was bent.

Gas Atomization of X6CrNiTi18-10 Stainless Steel Powder for Selective Laser Melting Technology

Powders of X6CrNiTi18-10 stainless steel were fabricated from original workpieces of different grade by gas atomization method. It was found that it is necessary to use argon as a gas for gas atomization of X6CrNiTi18-10 steel, since the use of nitrogen leads to the formation of its compounds, namely, titanium nitride. It is shown that all used workpieces – electric arc, electric slag and vacuum arc refinement – allow one to obtain powders suitable for further utilization in selective laser melting technology of 3D printing. The main physicochemical and technological properties of the obtained powders have been investigated. Changes in the chemical composition and quality of the powders are not significant within the X6CrNiTi18-10 grade. The 0...20 μm fraction of powders does not have fluidity, and thus cannot be used for additive technologies. The fraction 20...63 μm have suitable rheological properties for additive technologies and may be used in selective laser melting (SLM) process. The yield of target fraction 20 ... 63 microns was ≈45%. The fraction 63...120 μm may be used for the direct metal deposition (DMD) additive technology. Considering the economic aspect of the technology, it is preferable to use original workpieces of X6CrNiTi18-10 steel produced by electric arc or electroslag process, since the market price of vacuum arc steel is significantly higher. The fraction of ferrite phase in the powder increases with a decrease of particle size of the resulting powder and is lower comparing to the original workpiece. In the future, for a detailed study of the technological properties, it is planned to grow samples from each type of the obtained powders on installation for selective laser melting and direct laser deposition to determine the physical and mechanical properties of fabricated samples (tensile and impact bending tests) and carry out metallographic studies.

Microstructure formation mechanism and corrosion behavior of FeCrCuTiV two-phase high entropy alloy prepared by different processes

The microstructure and corrosion resistance of FeCrCuTiV high entropy alloy prepared by vacuum arc melting and laser melting deposition were studied. The microstructure and phase composition of FeCrCuTiV high entropy alloy were characterized by SEM, XRD, EBSD, etc. It is found that both of them are composed of the FCC Cu-rich phase, BCC Fe-rich phase and, BCC V-rich phase. Comparing with FeCrCuTiV high entropy alloy prepared by vacuum arc melting, the grain size of FeCrCuTiV high entropy alloy prepared by the laser melting deposition reduces from 29.48 µm to 1.85 µm. Meanwhile, the Cu-rich phase volume fraction decreases from 44.7 % to 31.5 %. Two reasons contribute to this phenomenon: On the one hand, the higher cooling rate of high entropy alloy makes the grain growth limited and the grain size reduced. On the other hand, the higher cooling rate reduces the volume fraction of intergranular segregation Cu-rich phase formed under non-uniform solidification due to the lack of long-range migration of Cu element, which makes the solidification state of FeCrCuTiV high entropy alloy prepared by laser melting deposition deviate from the ideal thermodynamic equilibrium. In addition, the corrosion resistance test of FeCrCuTiV high entropy alloy prepared by two processes indicates: FeCrCuTiV high entropy alloy prepared by laser melting deposition shows better corrosion resistance under the electrochemical corrosion of salt solution. This result is caused by the reduction of the Cu-rich phase, which weakens its corrosion effect as the anode of galvanic cell. Laser melting deposition technology provides new ideas and methods for controlling the phase structure of complex solid solution high entropy alloys to improve their physical properties.