Solid Forming Research Articles

Effect of heat treatment on microstructure and mechanical properties of 34CrNiMo6 steel by laser solid forming

34CrNiMo6 steel was fabricated by laser solid forming technology. The effect of quenching and tempering treatment on the microstructure and mechanical properties was studied. The results showed that the microstructure of as-deposited samples consisted of martensite and bainite and tempered martensite. After quenching and tempering, the microstructure of the deposited layer was finer and became uniform, which was mainly tempered sorbite. When the sample was quenched at 830 °C and tempered at 460 °C, the microstructure was the tempered martensite. With the increase of tempering temperature, the content of carbide precipitated in martensite gradually increased. With the increase of quenching temperature, hardness of the samples increased firstly and then decreased. The hardness of the deposited layer gradually decreased with increasing the tempering temperature. The best quenching and tempering process for the laser solid forming 34CrNiMo6 steel was 830 °C quenching +540 °C tempering, which differed from the tempering treatment process for forged parts. The tensile strength increased from 980 MPa under the standard quenching and tempering conditions to 1230 MPa (increased by 25.5%) and the yield strength increased from 916 MPa under the standard quenching and tempering conditions to 1123 MPa (increased by 22.6%). But the elongation and percentage reduction of area obtained by the two quenching and tempering conditions were basically the same. The mechanical properties of LSFed 34CrNiMo6 steel after the optimal tempering treatment process had reaches the forging standard. The fracture mode of heat-treated LSFed sample was ductile fracture.

Microstructure and Phase Transformation Temperature of NiTiNb Shape Memory Alloy Prepared by Laser Solid Forming Using Mixed Powder

NiTiNb is a wide-hysteresis shape memory alloy. The Laser Solid Forming (LSF) technology can overcome the shortcomings of the traditional long cycle processing to prepare NiTiNb. In this work, we studied the microstructure and phase transformation temperature of the NiTiNb prepared by LSF., in which the Ni + Ti + Nb mixed powder was melted under different laser power P, scanning speed v, layer thickness t, and energy density EV. The results show that the combination of LSF process parameters with P = 2000 W and v = 900 mm/min can obtain a good metallurgical bond. As the laser power increases, the grain size increases, and the proportion of equiaxed crystals increases, the martensite transformation temperature increases. The inhomogeneity of the LSF-NiTiNb microstructure results in different phase transformation temperatures even in the same sample. The subsequent heat treatment at 850 °C for 3 h increases the phase transformation temperature and hysteresis of LSF-NiTiNb. The tensile properties of the LSF-NiTiNb samples with different building heights are significantly different. The maximum elongation reaches 8% and the minimum elongation is only 0.8%. The LSF parameter combination in this work has reference value for the parameter selection of subsequent preparation of NiTiNb.

Effect of dimensionless heat input during laser solid forming of high-strength steel

Laser solid forming (LSF) technology can be used to rapidly manufacture and repair high-strength steel parts with superior performance, but the value of the heat input during operation is difficult to quantify, which has a substantial impact on the microstructure and mechanical properties of the parts. A promising method to improve the forming efficiency and quality of LSFed parts is to accurately control the heat input and explore its relationship with the microstructure and mechanical properties. To remove the interference of other variables from the experiment, the dimensionless heat input Q* was introduced. The Q* values were designed in advance to calculate the experimental parameters used to perform the LSF experiment. The microstructure was observed at different regions of the sample, and its mechanical properties were analyzed. From the results, the following conclusions were drawn. The Q* value was directly related to the cooling rate and heat accumulation in the top structure, leading to the formation of different microstructures; it also modified the original structure at the bottom, affecting the subsequent thermal cycle and indirectly changing the tempered martensite morphology. The heat input also affected the mechanical properties of the sample. The hardness of the stable zone decreased with increasing Q* value, and the lowest value was 190 HV. Similarly, the tensile strength and yield strength of the LSFed samples decreased considerably with increasing Q* value, and the lowest values were 735 and 604 MPa, respectively. Only the elongation and reduction in the area increased after a slight decrease. The Q* value had a significant effect on heat treatment. When Q* = 2.9, the increase in tensile strength and yield strength after heat treatment was the largest (29% and 44%, respectively).

A microcompression study on the mechanical properties and fracture behavior of Be–Al and Be–AlSi10Mg alloys fabricated by laser solid forming

The microstructure and micropillar compression responses of thin-walled Be–Al and Be–AlSi10Mg samples, produced by laser solid forming (LSF), were investigated. Both alloys resembled typical 3-D net-shaped structures. The Be–AlSi10Mg alloy exhibited coarser Be grains embedded in the refined Al net-like matrix owing to a broader solidification region. Owing to the multi-hardening by Si and Mg alloying, the yield strength of the system significantly increased from 150 MPa to 220 MPa. In addition, the failure mode changed from plastic fracture of the Al phase in Be–Al to brittle fracture of the Be phase in Be–AlSi10Mg during microcompression. Based on the theoretical calculation of the yield strength and fracture strength, grain size refinement by the non-uniform nucleation process was dominant factor affecting the Al matrix strength increment of Be–AlSi10Mg. Meanwhile, the critical resolved shear stress of Be was smaller than the ultimate strength of the Al phase strengthened by Si and Mg in the Be–AlSi10Mg alloy. Thus, the failure preferentially occurred in the Be phase rather than the Al phase. These results suggest that improving the fracture strength of the Be phase is important for obtaining high-performance Be–Al alloys after the strengthening of the Al phase by alloying additions and artificial aging measurements.

Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

ГЕНЕЗИС ЦІЛЕЙ І ЗАВДАНЬ ВИБУХОВОГО ШТАМПУВАННЯ (ДО 70-РІЧЧЯ ОДНІЄЇ З НАУКОВИХ ШКІЛ ХАІ)

The paper is devoted to development of one of the scientific schools Kharkiv Aviation Institute (Now National Aerospace University named after M. E. Zhukovsky “KhAI”). This school was born after World War II quite hard after period of National economy restoration and now it continues to develop during last 70 years. The article deals with the origins and genesis of objectives and tasks formulated for think tank and followers during dozens of years. Influence of the world geopolitics on development of mentioned scientific school and reached results is shown. From relatively primitive goals and tasks formulated by R. V. Pikhtovnikov in 1949 up to complicated problems of controlling of impulse energy flows to get high-precision large-dimensional sheet articles. From development of simple manufacturing process conducted in field conditions up to creation of up-to-date manufacturing complexes with correspondent buildings, equipment and technological jigs.Paper draws attention that successful development of scientific school and international expansion of labor market were stipulated by governmental support, both financial and organization ones. Paper shows results of technological systems development. Defefinite analogy with development of biological systems can be observed, i.e. evolution from the simplest to more complicated under influence of external factors.One has to note that paper deals with development of only one direction of scientific school, i.e. sheet articles forming. Research and development of such two other directions as impulse forming by impact of solid and impulse volumetric forming are waiting for their researchers. Authors of the paper tried to escape of conventional approaches of scientific schools description and concentrated on studying of objectives and tasks occurred in frames of considered scientific school. Therefore, the paper doesn’t mention many names of scientific advisors of different directions, titles of exact studies and topics, which involve crucial contribution in achievements of mentioned scientific school.

A Novel Ti-4.13Al-9.36V Alloy of High Ductility Designed on Base of α''-Microstructure for Laser Solid Forming

A Novel Ti-4.13Al-9.36V Alloy of High Ductility Designed on Base of α''-Microstructure for Laser Solid Forming

Effect of electrolyte solutions on the electrochemical dissolution behavior of additively manufactured Hastelloy X superalloy via laser solid forming

The electrolyte solution significantly affects electrochemical machining. This study investigates the electrochemical dissolution behavior of a laser solid formed Hastelloy X nickel-based superalloy in 15 wt% NaNO3, 7.5 wt% NaNO3 + 7.5 wt% NaCl, and 15 wt% NaCl solutions. The Cl- ions in the electrolyte solution accelerates the passive dissolution rate because the electrochemical reactions at the metal/film and film/solution interfaces are promoted. During the transpassive dissolution process, the Cl- ions in the electrolyte solution weaken the hindering effect of the transpassive film on the dissolution process, resulting in a faster transpassive dissolution rate and a higher current efficiency. Furthermore, the flatness of the dissolved surface in the chloride-containing solution is significantly higher than that in the chloride-free solution. Two models are proposed to illustrate the passive and transpassive dissolution behaviors. This study provides theoretical guidance for the selection of electrolyte solutions for the electrochemical machining of laser solid formed nickel-based superalloys.

Effect Analysis of Laser Shock Peening on Nickel-based Alloys by Laser Solid Forming

Laser solid forming has the advantages of rapid and complex shapes, but the stress caused by high temperature gradient changes during the forming process can easily lead to the deformation of parts and insufficient mechanical properties. This article focuses on laser solid forming GH4169 superalloy for laser shock peening. The influence of process parameters on surface morphology and toughness were analyzed. The mechanism of laser shock peening was analyzed. The results show: As the number of impacts increases, the depth gradually increases, and the increasing trend slows down. When the energy is small, the surface change cannot be observed. After 5J, as the energy increases, the depth of the pit increases. As the impact energy increases, the toughness of the material first increases and then decreases. The toughness of the material is the highest at 6J, reaching 65J/cm2. The action mechanism of laser shock peening has three main methods, one is fine-grain strengthening, the other is twinning and work hardening, and the third is stress strengthening.

Influence of processing parameters on deposition characteristics of Inconel 625 superalloy fabricated by laser solid forming

Influence of processing parameters on deposition characteristics of Inconel 625 superalloy fabricated by laser solid forming

Effects of Heat Treatments on Microstructures and Mechanical Properties of Ti6Al4V Alloy Produced by Laser Solid Forming

The steep thermal gradient and complicated thermal cycle occur in the fabrication of Ti6Al4V alloy during laser solid forming (LSF). That leads to obvious anisotropic mechanical properties and requires essential heat treatments to improve its performance. In this work, different heat treatment strategies under vacuum condition were used to study the evolution of microstructures and mechanical properties of Ti6Al4V alloy produced by LSF. The results show that transformation from α phase into lamellar α + β dual-phases structure is introduced at low temperature (550 °C), and the α phase is broken and refined at higher temperature (800 °C). Tensile tests present the increase of elongations in the horizontal and vertical directions by 12.4% and 13.2% for specimens treated by two-step heat treatment (750 °C × 4 h + 500 °C × 1 h). Fatigue crack growth (FCG) lives of LSFed Ti6Al4V alloy after different heat treatments were improved due to the elimination of residual tensile stress and the transformation of α phase into α + β dual-phase structure. Specimens treated at 800 °C for 4 h exhibit a higher fatigue life among those heat-treated alloys. The low sensitivities of the FCG behavior in the Paris-zone to different heat treatments under vacuum condition are explored in the FCG testing of Ti6Al4V alloy.

Grain refinement and improved tensile properties of Ti5Al2Sn2Zr4Mo4Cr titanium alloy fabricated by laser solid forming

Laser solid forming (LSF) Ti5Al2Sn2Zr4Mo4Cr titanium alloy usually exhibits brittle fracture with a poor elongation when the tensile direction is perpendicular to the growth direction of columnar β grains. In the present study, the effect of powder feed rate on the columnar to equiaxed transition (CET) and grain refinement of Ti5Al2Sn2Zr4Mo4Cr titanium alloy during the LSF process was investigated. The results showed that increasing in powder feed rate could effectively promote CET during LSF process. However, keeping increasing in the powder feed rate did not further refine the β grains effectively, especially in the regions near the fusion lines. The pauses of the LSF process aimed to obtain equiaxed β grains also lead to the precipitation of very fine α laths inside the β grains since the heat accumulation was avoided. The microstructure containing equiaxed β grains and homogeneous α laths was obtained after heat treatment. The tensile test was performed both in the vertical (parallel to the build direction) and horizontal (perpendicular to the build direction) directions under the as-deposited and heat treatment conditions. The tensile properties, especially the ductility, were significantly improved compared to that in the previous studies. It is partly because the equiaxed β grains effectively prevented the crack propagation.

Microstructure and mechanical properties of Be–Al alloy fabricated by laser solid forming

The microstructures and tensile mechanical properties of thin-walled Be-38 wt%Al samples produced by laser solid forming (LSF) are investigated. The results show that no cracking or significant porosity is observed in the thin-walled samples. The microstructure of the LSFed Be–Al alloy is primarily composed of columnar Be grains delineated by continuous Al networks. The columnar Be grains show almost the same crystallographic orientation, in which the preferred growth direction is the <0001> direction inclined towards the scanning direction at an angle of approximately 70°. The widths of the Be columnar grains gradually increase as the deposition height increases. The LSFed Be–Al alloy shows anisotropic tensile properties, exhibiting higher ultimate tensile strength and yield strength but smaller elongations for the longitudinal specimens compared to the transverse specimens. BeO and Al2O3 particles are observed to be primarily distributed at the Be/Al interface, resulting in a lack of bonding or cracking during the tensile test.

Passive behavior of nickel-based superalloys prepared by high-deposition-rate laser solid forming additive manufacturing

We report the crystallographic texture and passive behavior of nickel-based superalloys prepared by high-deposition-rate laser solid forming (HDR-LSF) additive manufacturing in deaerated 10 wt.% NaNO3. The HDR-LSF Alloy 718, mainly composed of columnar grains, is detected to be weakly fiber textured due to the direction changed structure. However, passive current densities on horizontal and vertical sections have no difference and both increase linearly with the electrode potential. Furthermore, the identical steady-state passive current density on both sections is attributed to the same film/solution interface energy. Amorphous structure of the bi-layer film induces the electrochemical activity isotropy regardless of matrix texture.

Influence of post-heat-treatment on the microstructure and fracture toughness properties of Inconel 718 fabricated with laser directed energy deposition additive manufacturing

The influence of post-heat-treatment on the resulting microstructure and room-temperature fracture toughness (KIC) of Inconel 718 fabricated by laser solid forming (LSF), a kind of laser based directed-energy-deposition additive manufacturing technologies, is investigated. Detailed microstructure characterization was performed on as-fabricated and heat-treated samples using direct aging (DA), solution treatment plus aging (STA), homogenization plus STA (HSTA), respectively. The results indicate that as-fabricated sample mainly consists of γ columnar dendrites and a small quantity of (γ+Laves) eutectics in the interdendritic areas. After DA post-heat-treatment, the nonuniform γ′′/γ′ precipitates exist around Laves phases. After STA post-heat-treatment, the short-acicular δ-phases precipitate around/in the Laves phases, the micro-segregation reduces and the distribution of γ′′/γ′ precipitates in the dendrite arm is almost homogeneous. After HSTA post-heat-treatment, Laves phase mostly disappears, micro-segregation completely removes and the γ′′/γ′ precipitates (~30 nm) are distributed in bimodal recrystallized grains. The results of KIC testing indicate that as-fabricated sample possesses the lowest KIC mainly due to its lowest elastic modulus and yield strength. However, the KIC of DA sample (~89.8 MPam) is close to that of as-fabricated sample, mainly due to its low ductility and strain-hardening exponent. But, the KIC of STA and HSTA samples increases by ~55.8% and 90.8% compared with as-fabricated sample respectively, mainly because of the better performance in strength–plasticity of HSTA sample (~1114 MPa, ~26.1%). Particularly, the KIC of HSTA sample with bimodal grains is ~60 MPam higher than the lower limit of wrought IN718 (AMS 5662) and reaches ~164.1 MPam. There exists significant difference in the KIC fractographs of as-fabricated and heat-treated samples. Overall, this research illustrates that an appropriate post-heat-treatment possesses obvious toughening effect on the LSF Inconel 718 alloy.

Microneedles in Smart Drug Delivery.

Significance: In biomedical setup, at large, and drug delivery, in particular, transdermal patches, hypodermal needles, and/or dermatological creams with the topical appliance are among the most widely practiced routes for transdermal drug delivery. Owing to the stratum corneum layer of the skin, traditional drug delivery methods are inefficient, and the effect of the administered therapeutic cues is limited. Recent Advances: The current advancement at the microlevel and nanolevel has revolutionized the drug delivery sector. Particularly, various types of microneedles (MNs) are becoming popular for drug delivery applications because of safety, patient compliance, and smart action. Critical Issues: Herein, we reviewed state-of-the-art MNs as a smart and sophisticated drug delivery approach. Following a brief introduction, the drug delivery mechanism of MNs is discussed. Different types of MNs, that is, solid, hollow, coated, dissolving, and hydrogel forming, are discussed with suitable examples. The latter half of the work is focused on the applied perspective and clinical translation of MNs. Furthermore, a detailed overview of clinical applications and future perspectives is also included in this review. Future Directions: Regardless of ongoing technological and clinical advancement, the focus should be diverted to enhance the efficacy and strength of MNs. Besides, the possible immune response or interference should also be avoided for successful clinical translation of MNs as an efficient drug delivery system.

Solidification Effect on the Microstructure and Mechanism of Laser‐Solid‐Forming‐Produced Flame‐Resistant Ti–35V–15Cr Alloy

Ti–35V–15Cr alloy has become an indispensable material in aerospace industry due to its excellent flame‐resistance properties. Herein, the block and thin‐wall Ti–35V–15Cr samples are built by laser solid forming (LSF) under the same processing parameters, and the evolution of solidification microstructure is investigated. This work focused on the effect of molten pool solidification parameters and complex thermal cycling conditions on the morphology of β grains and the substructure in the grains. The microstructure of LSF‐produced Ti–35V–15Cr block sample mainly consists of epitaxial columnar dendritic grains, whereas that of the deposited thin‐wall sample is mainly composed of near‐equiaxed grains together with subgrains formed in the near‐equiaxed grains. Such different microstructure results from extremely sensitive thermal behavior condition in LSF process. The simulated thermal behavior characteristics using finite element method illustrate that the thermal cycles during block deposition are very complex and the temperature gradient at the last solidification in block deposition is much higher than that in the deposition of thin‐wall samples, resulting in significantly different solidification microstructure between thin‐wall and block samples.

A Real-Time Method to Detect the Deformation Behavior during Laser Solid Forming of Thin-Wall Structure

Laser solid forming (LSF) is a promising additive manufacturing technology. In the LSF process, deformation behaviors dictate the accuracy of the produced parts. In this study, by using a laser displacement detector based on laser triangulation principle, an accurate and effective real-time detection method was established to monitor the real-time deformation behavior of the key position during the LSF of a thin-wall structure. The results confirmed that increasing thin-wall length results in increasing final deformation of the edge. The displacement fluctuation range and value in the middle of thin wall are both smaller than that of the positions near the end, while the entire displacement changing direction in the middle is opposite to that of the end positions. When the deposition process is paused, the deformation of the thin wall during the cooling stage will deviate the position of the deposited thin wall, resulting in the dislocation between the subsequent deposited part and that before the pause, which affect the dimensional accuracy of the thin wall structure. This non-contact real-time detection method also confirmed the ability to monitor the initiation of cracking during the LSF process, and a potential to be used for the on-line feedback control of deformation of detected key position of deposited structure.