Solid Forming Research Articles

Microstructure and flame-retardant properties of the TF550 titanium alloy by ultrasonic vibration assisted laser solid forming

More and more attention has been paid to the application of flame retardancy and surface strengthening of titanium alloys in the aerospace field. In this paper, ultrasonic vibration assisted the laser solid formed (LSFed) TF550 flame-retardant titanium alloy was studied, and the influence of ultrasonic vibration on the microstructure and flame-retardant properties of the LSFed TF550 alloy was analyzed. The results showed that the LSFed TF550 alloy after ultrasonic vibration treatment effectively reduced the generation of pores. When the ultrasonic amplitude was 60 μm, the porosity was the lowest. The porosity of the sample was reduced from 3.84 % to 0.53 %, with the reduction of 86 %. The ultrasonic vibration results in the CET transformation of LSFed TF550 alloy specimen, and the average grain length-width ratio decreases from 5.3 to 1.2, and the microstructure of the specimen changes from the average width of 214 μm to the average grain size of 144±12 μm. Especially when the ultrasonic amplitude is 90 μm, the equiaxial grain size and the grain length-width ratio are the lowest. The effect of ultrasonic vibration at different positions was different. The higher the deposition height, the more columnar crystals in the microstructure and the less equiaxed crystals. When the deposition height was 43 mm, equiaxed crystals and columnar crystals began to coexist. Due to the grain refinement effect of ultrasonic vibration, the number of grain boundaries was increased, and the flame-retardant properties of the LSFed TF550 alloy was improved.

Research Progress on the Manufacturing of Screw-Shaped Parts in Screw Compressors

Screw compressors are highly researched and developed prospects in industry because of their long service life, high transmission efficiency, low footprint and low vibration. As the key core part of the screw compressor, the screw is a typical, long-shaft, complex profile part. Its processing method, manufacturing accuracy and quality have an extremely important impact on the performance of the whole screw compressor. In this work, the research progress on the manufacturing of screw-shaped parts in screw compressors is summarised from the aspects of the cutting process, solid plastic forming, casting and additive manufacturing. The merits and demerits of these manufacturing processes are provided and discussed, which is conducive to the development of the high-efficiency, precise and high-performance forming process of screw-shaped parts. Additionally, a novel forming process is proposed to solve the problems of serious material waste and low production efficiency for the screw-shaped parts. In the proposed process, the semi-solid spherical grain is firstly prepared by radial forging and the isothermal treatment of long-shaft raw materials. The large strain energy can be stored in the bar by the radial forging of long-shaft raw materials, which is used to induce the generation of semi-solid spherical grains with the assistance of the isothermal procedure. After that, the screw is fabricated by the high-efficiency semi-solid closed extrusion process.

Microstructure and properties of Ti60 alloy by laser solid forming and ultrasonic impact hybrid manufacturing

The hybrid manufacturing of laser solid forming (LSF) and ultrasonic impact treatment (UIT) was used to improve the structure and properties of Ti60 alloy by strengthening the surface layer-by-layer. The microstructure, mechanical properties, and burn resistance of LSFed Ti60 samples before and after UIT by SEM, TEM, and XRD were analyzed and compared. The results showed that the grains of LSFed Ti60 alloy were refined and metallurgical defects were reduced after the UIT process. Meanwhile, the deposited layer was severely deformed after UIT and nanocrystals were formed on the surface. In addition, the microhardness of the deposition layer surface increased and the residual stress changed from tensile stress to compressive stress. The area of the ablation hole was reduced by 21% and the proportions of Mo, Nb, and Zr elements increased. In summary, hybrid manufacturing of LSF and UIT can improve the microstructure and properties of LSFed Ti60 samples.

Effect of TiB2 content on microstructure and mechanical properties of GH3536 superalloy formed by laser solid forming

In this paper, GH3536 and TiB2/GH3536 alloys were prepared by laser solid forming(LSF). The effects of TiB2 content on the microstructure and mechanical properties of as-deposited samples were investigated. The results show that, with the increase of TiB2 content in the as-deposited samples, the molten pool boundary becomes shallower, the dendrite structure grows coarser, and the grain size gets larger. Meanwhile, phase segregation intensifies at the interdendritic and grain boundaries. The shape and types of the precipitated phases change significantly: the strip M23C6 carbide phase progressively evolves into a network phase of M23C6 carbide, M2B boride, and Mo-rich phase. Besides, the grain size of the solid-solution samples becomes smaller, and the columnar grains in both sample groups tend to be equiaxed. Interdendritic precipitates undergo a morphological change from a continuous network to a granular one as they gradually dissolve into the matrix. The microhardness of both sample groups also rises, and their elongation gradually declines as the amount of TiB2 increases. However, the tensile strength trend exhibits the opposite fluctuation, as the tensile strength of as-deposited samples drops and that of solid-solution samples increases with the increase of TiB2 content.

Z-Increments Online Supervisory System Based on Machine Vision for Laser Solid Forming.

An improper Z-increment in laser solid forming can result in fluctuations in the off-focus amount during the manufacturing procedure, thereby exerting an influence on the precision and quality of the fabricated component. To solve this problem, this study proposes a closed-loop control system for a Z-increment based on machine vision monitoring. Real-time monitoring of the precise cladding height is accomplished by constructing a paraxial monitoring system, utilizing edge detection technology and an inverse perspective transformation model. This system enables the continuous assessment of the cladding height, which serves as a control signal for the regulation of the Z-increments in real-time. This ensures the maintenance of a constant off-focus amount throughout the manufacturing process. The experimental findings indicate that the proposed approach yields a maximum relative error of 1.664% in determining the cladding layer height, thereby enabling accurate detection of this parameter. Moreover, the real-time adjustment of the Z-increment quantities results in reduced standard deviations of individual cladding layer heights, and the height of the cladding layer increases. This proactive adjustment significantly enhances the stability of the manufacturing process and improves the utilization of powder material. This study can, therefore, provide effective guidance for process control and product optimization in laser solid forming.

Achieving superior burn resistant and mechanical properties of Ti40 alloy by laser solid forming

Laser solid forming (LSF) technology had a great influence on the manufacturing of aeronautical burn resistant titanium alloy Ti40, which was related to the comparison and competition between additive manufacturing and traditional forging parts. The Ti40 deposition blocks were fabricated using the LSF technique and tested for microstructure, mechanical properties and burn resistance. The results showed that, compared with the forged sample, the grain of LSFed sample was refined to a certain extent, and α phase and Ti5Si3 phase were precipitated. The tensile and yield strengths of the LSFed Ti40 alloy were 965 MPa and 962 MPa, respectively, which were higher than those of the forgings, and the elongation was close to that of the forgings. The fracture mechanism was a mixture of ductile and brittle fractures. The area and depth of the ablation pit and the area of the thermal zone of influence in the LSFed sample were smaller than in the bifurcated state. The Ti5Si3 precipitated in the LSFed sample not only improved the oxidation efficiency of the V and Cr elements by retaining the pores, but also slowed down the spallation of the oxide layer by strengthening the binding of the matrix to the oxide layer and improved the burn resistance of Ti40. Overall, the tensile strength and elongation of the LSFed Ti40 alloy were up to the forging standard, and the burn resistance was better than that of the forged Ti40 alloys.

Phase equilibria and microstructure development in Mg-rich Mg-Gd-Sr alloys: Experiments and CALPHAD assessment

Mg-Sr alloys are promising to fabricate orthopedic implants. The alloying of rare earth elements such as Gd may improve the comprehensive mechanical properties of Mg-Sr alloys. The information on the phase diagram and the microstructure development are required to design chemical composition and microstructure of Gd alloyed Mg-Sr alloys. The phase equilibria and the microstructure development in Mg-rich Mg-Gd-Sr alloys (Gd, Sr < 30 at. %) are experimentally investigated via phase identification, chemical analysis, and microstructure observation with respect to the annealed ternary alloys. The onset temperatures of liquid formation are measured by differential scanning calorimetry. A thermodynamic database of the Mg-rich Mg–Gd–Sr ternary system is developed for the first time via CALPHAD (CALculation of PHAse Diagram) approach assisted by First-Principles calculations. The thermodynamic calculations with the developed database enable a well reproduction of the experimental findings and the physical-metallurgical understanding of the microstructure formation in solidification and annealing.

Prediction of molten pool temperature in laser solid forming based on PSO-LSTM

The temperature of the molten pool in Laser Solid Forming has a direct effect on the dimensional accuracy and mechanical properties of the parts. Accurate prediction of the melt pool temperature is important to ensure the stability of the melt pool temperature and to improve the forming accuracy and quality of the part. In order to accurately predict the melt pool temperature, this study proposes a melt pool temperature prediction method based on particle swarm optimization (PSO) optimised long short-term memory neural network (LSTM). Using IR camera to obtain melt pool temperature data and establish long short-term memory neural network melt pool temperature prediction model based on experimental data. Optimization of the initial learning rate and the number of hidden layer units of the long short-term memory neural network model using the particle swarm optimization algorithm to build a PSO-LSTM model for prediction of melt pool temperature. The results show that the PSO-LSTM prediction model outperforms the long short-term memory neural network and Ridge Regression models in all evaluation indicators and can achieve accurate prediction of melt pool temperature.

Effect of Solution Aging Heat Treatment on Microstructure Evolution and Properties of TC17 Titanium Alloy Formed by Laser Solid Forming

Effect of Solution Aging Heat Treatment on Microstructure Evolution and Properties of TC17 Titanium Alloy Formed by Laser Solid Forming

Effect of Deposition Thickness on the Microstructure of Laser Solid Forming 34CrNiMo6 Steel

Effect of Deposition Thickness on the Microstructure of Laser Solid Forming 34CrNiMo6 Steel

Effect of Al–5Ti–0.3C–0.2B Master Alloy on the Structure and Properties of Ti6Al4V by Laser Solid Forming

Titanium matrix composites (TMCs) with the addition of in situ ceramic reinforcing particulates have attracted extensive interest. Herein, additive‐manufactured Ti6Al4V/Al–5Ti–0.3C–0.2B alloys are fabricated from mixed powders by laser solid forming. The contents of Al–5Ti–0.3C–0.2B with 1.5, 2.5, and 5.0 wt% are considered. The results indicate the apparent microstructure transition from columnar grain to equiaxed grain with increasing content of Al–5Ti–0.3C–0.2B. The in situ reaction between the Ti6Al4V and Al–5Ti–0.3C–0.2B produces TiB, TiC, and Ti3AlC reinforcements. The increase of Al–5Ti–0.3C–0.2B content will refine grains and reduce α′ martensite phase, which is associated with the formation of TiB at the grain boundaries. As the content of Al–5Ti–0.3C–0.2B increases, the ultimate tensile strength of Ti6Al4V–x wt% (Al–5Ti–0.3C–0.2B) alloy increases from 993.8 MPa to 1233.6 MPa. The strength increases because of an increase of the solid phases TiB and Ti3AlC, which is ascribed to the presence of precipitation and grain refinement strengthening mechanisms. Meanwhile, the elongation of the alloy increases from 1.1% to 4.9% because the Ti3AlC phase is conducive to reducing thermal transfer and interfacial stress. These findings provide insights into the selection of reinforcement materials for optimizing mechanical properties of TMCs alloys.

Titanium clad plate forming: critical consideration and how different it is from solid titanium forming

Titanium offers exceptional corrosion resistance both in organic & inorganic acid media. Thus, it is a preferred material by various industries such as Oil and Gas refining, Petrochemical (PTA Plant) including Nickel refining by Hydrometallurgy. These equipment are operated at high temperature and pressure, necessitating the use of higher thickness for safety and efficient functioning. Therefore, use of solid titanium is not economical, and often substituted with explosion bonded Ti-Clad steel. Fabrication of certain components of this equipment like Dished heads are required to be made by forming with options of cold, warm or hot forming. Selection of forming method for Ti-clad steel component is often governed by its effect on Clad-Base metal bond integrity and reduction shear strength unlike other commonly used Stainless steel or Ni-based alloy clad material, wherein thickness of the base metal is major deciding factor. In case of Ti-Clad steels both cladding and base metal are not metallurgically compatible as well as differs significantly in their physical properties, forming temperature plays a crucial role. This paper describes the effect of various Dished heads forming methodology on integrity of clad plate. Also, it brings out how the Ti-clad steel forming is critical than the forming of solid Titanium.

Electrochemical properties and dissolved behavior of laser solid formed Ti6Al4V alloy in NaCl solution with different current densities

The hybrid manufacturing process of additive manufacturing (AM) and electrochemical machining (ECM) is a new approach to advanced manufacturing technology. The feasibility of using ECM to machine an as-deposited Ti6Al4V alloy fabricated by the laser solid forming (LSF) method of AM was investigated in 15 wt.% NaCl solution. As the machining current density increased, the material removal rate increased linearly, and the current efficiency dropped from 140% to 93%. The current efficiency over 100% at low current densities was attributed to the electrochemical reactions of atoms in lower valence states. The microdissolved grooves, resulting from selective preferential dissolution of the α phase, were shallowed when machined at a higher current density (>3 A cm −2 ) and are attributed to the weakening of the galvanic effect at higher machining voltages. Additionally, the dissolved surface topography exhibited the worst waviness at the delimited current density of 10 A cm −2 , and the surface waviness decreased rapidly as the current density increased in the positive delimited range. Considering the machining efficiency and the surface quality of ECM, the as-deposited Ti6Al4V machined at a current density of 40 A cm −2 will be the preferred ECM current parameter.

Enhanced Strength and High-Temperature Wear Resistance of Ti6Al4V Alloy Fabricated by Laser Solid Forming

Abstract Strengthening titanium alloys and mitigating their wear degradation at various temperatures is the key to industrial applications. In this study, high-performance Ti6Al4V alloy (here, Ti with 6.25 wt% Al and 4.17 wt% V) was prepared by laser solid forming (LSF). The phase and microstructure of the Ti6Al4V alloys were systematically examined, and the overall improved mechanical properties were achieved. The coefficient of friction (CoF) and wear of LSFed Ti6Al4V alloy against WC-6%Co cemented carbide using a ball-on-disc tribometer at various temperatures revealed a temperature-dependent wear mechanism. During the experiment, the CoF of LSFed Ti6Al4V would increase initially and then decrease with the increased temperature. This trend is determined by the abrasive wear dominating at a lower temperature, and it gradually changes to oxidative wear and fatigue wear under higher temperatures. LSF provides a promising way to achieve supreme mechanical and tribological properties in Ti6Al4V simultaneously.

Effect of TiC on microstructures and mechanical behaviors of low-density Nb-Ti-Al alloys fabricated by laser solid forming

Ultra-high temperature Nb alloys are prospective for practical applications as aircraft materials. Sufficient efforts must be made to improve their manufacturing technologies and properties. The Nb-Ti-Al alloys with TiC addition were fabricated by laser solid forming (LSF) in this work. LSFed Nb-Ti-Al-TiC alloys which were composed of Nbss and (Nb,Ti)C had excellent formability and metallurgical quality. There were columnar and equiaxed Nbss grains in Nb-37Ti-10Al-3TiC and Nb-37Ti-10Al-5TiC while there were entire equiaxed Nbss grains in Nb-37Ti-10Al-8TiC. Expectant columnar-to-equiaxed transition was realized by the addition of TiC. Moreover, the grain sizes gradually decreased from the addition of 3TiC to 8TiC, and the average grain size of Nb-37Ti-10Al-8TiC decreased to 22.08 μm. The strip-like and particle-like (Nb,Ti)C precipitation coexisted in Nb-37Ti-10Al-3TiC and Nb-37Ti-10Al-5TiC, but only particle-like (Nb,Ti)C formed in Nb-37Ti-10Al-8TiC. The tensile strength, compression strength and fracture toughness of all Nb-Ti-Al-TiC alloys increased with the increase of TiC content. For Nb-37Ti-10Al-8TiC, the maximum tensile strength of 754.14 ± 3.84 MPa, compression strength of 3310.0 ± 55.28 MPa and fracture toughness of 34.96 MPa·m1/2 were obtained. The simultaneous increase of strength and fracture toughness was mainly attributed to fine grain strengthening by TiC addition. Compared with Nb alloy with the addition of Ta, W, Mo and Hf, the LSFed Nb-Ti-Al-TiC alloy had considerably high strength and was of low density. This confirmed the feasibility of preparing Nb alloy by LSF technology and adjusting the microstructure and property.

Influence of processing parameter on phase transformation and superelastic recovery strain of laser solid forming NiTi alloy

NiTi alloys with superelasticity and shape memory effects are currently widely used because of its excellent deformation recovery ability, mechanical strength, and biocompatibility. The Ni 50.8 Ti 49.2 alloy was manufactured by using laser solid forming (LSF) technology with pre-alloyed powder in this work. The microstructure, phase transformation and shape recovery of the deposited alloy were influenced by the parameters used in depositing process. The as-deposited Ni 50.8 Ti 49.2 alloy formed by LSF is columnar crystals epitaxially grown along the deposition direction, with a small amount of equiaxed crystals appear between the deposition layers. Two-step/multi-step martensitic transformation occurs in the deposited Ni 50.8 Ti 49.2 alloy. The martensitic transformation temperature slightly changes with the deposition height, whereas the R transformation temperature basically does not change with the deposition height. In the test of the mechanical properties, sample with a laser power of 1700 W and a scanning rate of 680 mm/min has a compression superelastic recovery as high as 9.5%. Moreover, Ti 2 Ni precipitated phase and R phase appeared in all samples, but only the precipitated Ti 2 Ni and R phase in this sample had a certain orientation relationship with the matrix. Shape memory characteristics was also tested by compression deformation, and the maximum recovery strain of shape memory effect is 6.1%, which is obtained in the sample deposited with 1500 W laser power and 480 mm/min scanning rate. • Columnar crystals grow along the deposition direction in LSF Ni 50.8 Ti 49.2 alloy. • Superelastic recovery as high as 9.5% was obtained in LSF Ni 50.8 Ti 49.2 alloy. • Orientation relationship of precipitation with matrix leads to high recovery rate.

Study on the micro-structure and the nano-indentation responses of laser solid formed epitaxial Ni-based superalloy

Laser solid forming (LSF) is one of the most promising technologies which has been extensively applied for the reshape and fabrication of the thermal parts in gas turbine and aero-engine. In this paper, the Ni-based single crystal superalloy thin-walled parts were prepared by using the LSF technology. Then, the electron back-scatter diffraction (EBSD) and the scanning electron microscope (SEM) technologies were employed to characterize the micro-structure morphology and crystallographic orientation of grains. The dislocation density of Ni-based superalloy thin-walled parts was analyzed. The results showed that a remarkable micro-structure gradient with respect to different heights of repaired Ni-based superalloy thin-walled parts was observed after the LSF process while the micro-structure distribution in width direction is comparatively more uniform. In addition, the misorientation of crystallographic orientation can be attributed to the dislocation density. A higher dislocation density contributes to aggregation of massive low angle grain boundaries (LAGBs) and formation of high angle grain boundaries (HAGBs), which in return conversely reduces dislocation density within the material. Finally, the mechanical properties of the LSF epitaxial Ni-based superalloy were investigated by the cyclic creep and Nano-indentation tests. The results showed that with the increasing of repair height, the residual indentation depth increased, while the elastic modulus increased first and then decreased. Meanwhile, a lower hardness of the stray grain region was obtained comparing with that of the substrate. Within the stray grain region, the hardness decreases along the building direction.

Microstructure and mechanical properties of crack - free Ni - based GH3536 superalloy fabricated by laser solid forming

Laser solid forming (LSF) was used to fabricate dense and crack-free specimens from solution-strengthened nickel-based superalloy GH3536 in this study. Tensile, and fatigue crack growth (FCG) testing was carried out in both horizontal and vertical build orientations with the condition at 25 °C and 500 °C. Three regions can be detected in the specimen: the additive manufacturing zone (AM), the heat affected zone (HAZ) and the substrate. M23C6 and M6C carbides were found in the specimens, only a small amount of hole defects was observed in the samples, and no cracks were found. The tensile test results show that the specimens have obvious anisotropy, and the horizontal specimens displayed higher strength (up to 855.3 MPa ultimate tensile strength at 25 °C). It is worth noting that there is no obvious anisotropy in the FCG rates of the specimens in different directions, and only when the ΔK is about 45–60 MPa m1/2, the FCG rates of the vertical specimens are higher. The increase in temperature will significantly reduce the tensile performance and increase the FCG rate of the specimens.

Study on Phase Transformation and Electrochemical Corrosion of TiNi Alloy Formed by Laser Solid Forming

TiNi shape memory alloy (SMA) prepared by laser solid forming (LSF) has wide application prospect and research value. In this work, LSF-Ti49.2Ni50.8 alloy was tested by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The microscopic characterization results show that there is a small amount of martensitic slat in TiNi alloy besides the TiNi substrate. Lenticular R phase is densely distributed around the martensitic slat. B2→R and R→M phase transitions occur in the alloy due to the high cooling rate during laser solid forming. The results of methyl thiazolyl tetrazolium (MTT) assay and electrochemical corrosion test show that the alloy has good biocompatibility and excellent corrosion resistance and has the potential to be used as a biomedical material.

Effect of electropulsing on the solidification of mould flux

The effect of electropulsing on the microstructure formation in solidification of mould flux has been investigated. Experimental characterization and image analysis reveals that the electropulsing treatment reduces 46% porosity and increases the interfacial perimeter to area ratio by 100%. The latter provides strong evidence that electric current influences interfacial energy. Dendrite arm spacing is reduced considerable. Electropulsing promotes the anisotropic crystal growth and retards the formation of interconnected crystal network. The latter is favourable to the current flow, liquid refilling and lubrication. The work demonstrates that electropulsing can be used to modify the microstructure of slag and hence to control the horizontal heat transfer rate in the mould, which is desirable in continuous casting of advanced high strength steels.