Showing papers on "Forging published in 2020"

High-strength Damascus steel by additive manufacturing

Abstract: Laser additive manufacturing is attractive for the production of complex, three-dimensional parts from metallic powder using a computer-aided design model1–3 The approach enables the digital control of the processing parameters and thus the resulting alloy’s microstructure, for example, by using high cooling rates and cyclic re-heating4–10 We recently showed that this cyclic re-heating, the so-called intrinsic heat treatment, can trigger nickel-aluminium precipitation in an iron–nickel–aluminium alloy in situ during laser additive manufacturing9 Here we report a Fe19Ni5Ti (weight per cent) steel tailor-designed for laser additive manufacturing This steel is hardened in situ by nickel-titanium nanoprecipitation, and martensite is also formed in situ, starting at a readily accessible temperature of 200 degrees Celsius Local control of both the nanoprecipitation and the martensitic transformation during the fabrication leads to complex microstructure hierarchies across multiple length scales, from approximately 100-micrometre-thick layers down to nanoscale precipitates Inspired by ancient Damascus steels11–14—which have hard and soft layers, originally introduced via the folding and forging techniques of skilled blacksmiths—we produced a material consisting of alternating soft and hard layers Our material has a tensile strength of 1,300 megapascals and 10 per cent elongation, showing superior mechanical properties to those of ancient Damascus steel12 The principles of in situ precipitation strengthening and local microstructure control used here can be applied to a wide range of precipitation-hardened alloys and different additive manufacturing processes A Damascus-like steel consisting of alternating hard and soft layers is created by using a laser additive manufacturing technique and digital control of the processing parameters

Hot forging wire and arc additive manufacturing (HF-WAAM)

Abstract: In this study, we propose a new variant of wire and arc additive manufacturing (WAAM) based on hot forging. During WAAM, the material is locally forged immediately after deposition, and in-situ viscoplastic deformation occurs at high temperatures. In the subsequent layer deposition, recrystallization of the previous solidification structure occurs that refines the microstructure. Because of its similarity with hot forging, this variant was named hot forging wire and arc additive manufacturing (HF-WAAM). A customized WAAM torch was developed, manufactured, and tested in the production of samples of AISI316L stainless steel. Forging forces of 17 N and 55 N were applied to plastically deform the material. The results showed that this new variant refines the solidification microstructure and reduce texture effects, as determined via high energy synchrotron X-ray diffraction experiments, without interrupting the additive manufacturing process. Mechanical characterization was performed and improvements on both yield strength and ultimate tensile strength were achieved. Furthermore, it was observed that HF-WAAM significantly affects porosity; pores formed during the process were closed by the hot forging process. Because deformation occurs at high temperatures, the forces involved are small, and the WAAM equipment does not have specific requirements with respect to stiffness, thereby allowing the incorporation of this new variant into conventional moving equipment such as multi-axis robots or 3-axis table used in WAAM.

Mg-Alloys for Forging Applications - A Review

Abstract: Interest in magnesium alloys and their applications has risen in recent years. This trend is mainly evident in casting applications, but wrought alloys are also increasingly coming into focus. Among the most common forming processes, forging is a promising candidate for the industrial production of magnesium wrought products. This review is intended to give a general introduction into the forging of magnesium alloys and to help in the practical realization of forged products. The basics of magnesium forging practice are described and possible problems as well as material properties are discussed. Several alloy systems containing aluminum, zinc or rare earth elements as well as biodegradable alloys are evaluated. Overall, the focus of the review is on the process control and processing parameters, from stock material to finished parts. A discussion of the mechanical properties is included. These data have been comprehensively reviewed and are listed for a variety of magnesium forging alloys.

Enhancing high-temperature strength of (B4C+Al2O3)/Al designed for neutron absorbing materials by constructing lamellar structure

Abstract: Aiming at developing new generation of high-temperature neutron absorbing materials for both structural and functional usages, (B4C + Al2O3)/Al composites were fabricated. Hot forging and extruding were carried out to adjust the microstructures of the composites. The forged samples exhibited a lamellar structure with Al2O3 staying at the grain boundaries. In the extruded sample, most Al2O3 entered into the interior of ultrafine-grains. Different strengthening effects of intergranular and intragranular Al2O3 at room and high temperatures were studied. It was verified that Al2O3 distributed at the grain boundaries was more beneficial to enhance the high-temperature strength by strengthening the grain boundaries and preventing dislocations from annihilating, therefore the forged samples were much stronger than the extruded sample at 375 °C. The sample forged with a height reduction ratio of 8:1 showed an ultimate strength of 342 MPa at room temperature and an ultimate strength of 96 MPa at 375 °C.

Increasing strength and ductility of a Mg–9Al alloy by dynamic precipitation assisted grain refinement during multi-directional forging

Abstract: A fine-grained microstructure with enhanced strength and ductility was fabricated in a Mg–9Al alloy by tailoring multi-directional forging with dynamic precipitation. The dynamic precipitation concurred with dynamic recrystallization and inhibited grain growth, thus improved the strength by grain boundary strengthening. The improved ductility was explained by the drastic morphology alteration and decreased volume fraction of the precipitates.

Assessment of laser power and scan speed influence on microstructural features and consolidation of AISI H13 tool steel processed by additive manufacturing

Abstract: Additive manufacturing can produce parts with complex geometries in fewer steps than conventional processing, which leads to cost reduction and a higher quality of goods. One potential application is the production of molds and dies with conformal cooling for injection molding, die casting, and forging. AISI H13 tool steel is typically used in these applications because of its high hardness at elevated temperatures, high wear resistance, and good toughness. However, available data on the processing of H13 steel by additive manufacturing are still scarce. Thus, this study focused on the processability of H13 tool steel by powder bed fusion and its microstructural characterization. Laser power (97−216 W) and scan speed (300−700 mm/s) were varied, and the consolidation of parts, common defects, solidification structure, microstructure, and hardness were evaluated. Over the range of processing parameters, microstructural features were mostly identical, consisting of a predominantly cellular solidification structure of martensite and 19.8 %–25.9 % of retained austenite. Cellular/dendritic solidification structure displayed C, Cr, and V segregation toward cell walls. The thermal cycle resulted in alternating layers of heat-affected zones, which varied somewhat in hardness and microstructure. Retained austenite was correlated to the solidification structure and displayed a preferential orientation with {001}//build direction. Density and porosity maps were obtained by helium gas pycnometry and light optical microscopy, respectively, and, along with linear crack density, were used to determine appropriate processing parameters for H13 tool steel. Thermal diffusivity, thermal conductivity, and thermal capacity were measured to determine dimensionless processing parameters, which were then compared to others reported in the literature.

Solid-state additive manufacturing high performance aluminum alloy 6061 enabled by an in-situ micro-forging assisted cold spray

Abstract: Cold spraying is a competitive additive manufacturing method featuring several unique characteristics and allows large-scale production of metallic components from a wide range of materials. In literature, high performance cold sprayed aluminum deposits produced using high-cost helium gas have been qualified for various applications. In this study, high performance aluminum alloy 6061 (AA6061) deposits were produced through a cold spray method using low-cost nitrogen gas enabled by an in-situ micro-forging effect (MF-CS). Results show that the MF-CS AA6061 deposit presents very low porosity as well as high ultimate tensile strength (UTS) and elastic modulus (E). Moreover, the MF-CS AA6061 deposit consists of superior equiaxed submicron fine Al grains with random orientations. However, the severe work hardening induced by intensive particle plastic deformation during deposition leads to very low ductility of the MF-CS AA6061 deposit. To eliminate this limitation, three strategies of heat treatments (stress relieving, recrystallization annealing and T6) were performed to the MF-CS AA6061 deposit. It was found that heat treatment generated complex effects on both inter-particle bonding and inner-particle microstructure (grain size, dislocation density and precipitation) and different strategies lead to different mechanical properties of AA6061 deposits. Among them, T6 heat-treated AA6061 deposits give the best overall mechanical properties with comparable UTS and E and only slightly inferior ductility to the corresponding T6 bulk.

High strength and plastic deformability of Mg–Li–Al alloy with dual BCC phase produced by a combination of heat treatment and multi-directional forging in channel die

Abstract: Mg–Li–Al (LA143) alloys with high strength and plastic deformability were prepared through a combination of heat treatment and multi-directional forging in a channel die (MDFC). The Vickers hardness of the alloy depended on the quenching temperature. As the applied equivalent strain was increased, the Vickers hardness and yield strength increased. The maximum specific yield strength of the Mg–Li–Al alloy in this study was 263 kN·m·kg -1 . The limit of reduction during cold rolling of all MDFCed LA143 samples exceeded 99%. X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy, revealed that the high specific yield strength could be attributed to severe plastic deformation as well as spinodal decomposition of the body-centered cubic phase. Therefore, LA143 alloys with excellent mechanical properties can be prepared by heat treatment and severe plastic deformation.

Repairing of exit-hole in dissimilar Al-Mg friction stir welding: process and microstructural pattern

Abstract: The exit-hole is one major discontinuities in the friction based processes, where all the volume of the tool’s probe is missing with a depth that corresponds to the full thickness of the processed component. This letter presents a new technique to repair the exit-hole of an Al-Mg friction stir welding, without any third body material with inexpensive probeless tooling, inducing forging, stirring, and thermomechanical consolidation of the local spot joint. Intercalated banned type structures with interpenetrating features were achieved. Composite type mixed structure was obtained at repaired zone with a local tensile strength of 159 MPa.

Structure-property relationships in hot forged AlxCoCrFeNi high entropy alloys

Abstract: AlxCoCrFeNi is one of the most extensively studied high entropy alloy systems, as it has shown excellent mechanical properties suitable for structural applications. In this work, AlxCoCrFeNi(x = 0.3, 0.5, 0.7) alloys were successfully hot-forged without any visible cracks. Contributions from different strengthening mechanisms were estimated and compared with the experiment. Optical microscopy, x-ray diffraction (XRD), electron backscatter diffraction (EBSD), energy dispersive x-ray spectroscopy (EDS) and hardness tests were used for structural and mechanical property analysis. A single-phase face centered cubic (FCC) structured was observed in the as-cast Al0.3 alloy, whereas, dual-phase FCC and body centered cubic (BCC) structures were observed in the as-cast Al0.5 and Al0.7 alloys. An increase in the FCC phase fraction was observed in all the alloy compositions after forging. Microstructure analysis revealed that phase fraction, the formation of twins, low angle grain boundaries, and grain refinement played a vital role in strengthening the alloy systems. After forging, the hardness of the Al0.3 and Al0.5 alloys was increased by 22% and 48%, respectively. In contrast, a reduction of 8% in hardness was observed in Al0.7 alloy. Reduction in the hardness is mainly due to higher FCC phase fraction and interface stress in forged Al0.7 alloy. A new modified rule of mixture is proposed to estimate the total strength of dual-phase high entropy alloys.

Effect of vanadium on microstructure and mechanical properties of bainitic forging steel

Abstract: This investigation attempts to thoroughly explore the effect of microalloying element V on the microstructural characteristics and mechanical properties of 20Mn2SiCrS bainitic forging steel. The results show that the cooling rate range of bainitic transformation was broadened with a 0.13% V addition and mainly a granular bainite microstructure was obtained after post-forging continuous cooling. The addition of V could refine the martensite/austenite (M/A) constituent and inhibit the formation of pro-eutectoid ferrite. Physical-chemical phase analysis revealed that only ~8.5% of the added V was in the V(C,N) precipitate in the as-forged condition, which resulted in relatively small precipitation strengthening (~40 MPa) compared with that in ferritic-pearlitic medium carbon forging steel. The addition of V can enhance the overall mechanical properties of the steel and it is concluded that the primary role of V in the as-forged bainitic forging steel is mainly to promote the formation of bainite and to refine the microstructure especially the M/A constituents as well as to resist softening of the M/A during the post-forging continuous cooling or during subsequent tempering when tempering treatment is necessary.

Hot deformation behaviour of 40CrNi steel and evaluation of different processing map construction methods

Abstract: 40CrNi steel is a low alloy steel with medium hardenability and has been widely used in the manufacturing of crankshafts, wind turbine forgings, etc. As forging is usually involved in the manufacturing of these components, optimization of the hot deformation process of 40CrNi steel is quite critical. Towards this, the prediction of flow stress and the determination of optimal processing parameter windows are of great importance. In this research, isothermal uniaxial hot compression tests were carried out for 40CrNi steel with true strain rates of 0.01, 0.1, 1, 10 and 30 s−1 and temperatures of 850–1200 °C. Both the strain compensated hyperbolic sine constitutive equation and the modified Johnson-Cook model were adopted to predict the flow stress curves, with average absolute relative errors of 0.034 and 0.061, respectively. Processing maps of the tested steel were constructed to determine the optimal deformation parameter windows, and the characteristics of the prior austenite microstructure generally correspond very well to the processing map established. Furthermore, different processing map construction methods were compared and it was found that power-dissipation efficiency maps strongly rely on the σ- e ˙ relationship. Assuming a certain type of constitutive equations leads to monotonic efficiency value patterns. Calculation methods based on experimental results are helpful to reflect the meaningful information carried by the experimental σ- e ˙ relationships.

Strengthening Mechanisms in Nickel-Copper Alloys: A Review

Abstract: Nickel-Copper (Ni-Cu) alloys exhibit simultaneously high strength and toughness, excellent corrosion resistance, and may show good wear resistance. Therefore, they are widely used in the chemical, oil, and marine industries for manufacturing of various components of equipment, such as: drill collars, pumps, valves, impellers, fixtures, pipes, and, particularly, propeller shafts of marine vessels. Processing technology includes bar forging, plate and tube rolling, wire drawing followed by heat treatment (for certain alloy compositions). Growing demand for properties improvement at a reduced cost initiate developments of new alloy chemistries and processing technologies, which require a revision of the microstructure-properties relationship. This work is dedicate to analysis of publicly available data for the microstructure, mechanical properties and strengthening mechanisms in Ni-Cu alloys. The effects of composition (Ti, Al, Mn, Cr, Mo, Co contents) and heat treatment on grain refinement, solid solution, precipitation strengthening, and work hardening are discussed.

Second phase particles and mechanical properties of 2219 aluminum alloys processed by an improved ring manufacturing process

Abstract: 2219 Al alloy has been used to manufacture the launch vehicle storage tank transition ring, but the large ring obtained in conventional manufacturing processes still suffers from severely agglomerated coarse second phase particles and poor mechanical properties. An improved process (forging at 510 °C with 20% deformation and at 240 °C with 50% deformation, then rolling at 240 °C with 30% deformation, followed by solid solution at 538 °C for 4 h and T8 treatment) for 2219 Al alloy large ring manufacturing was proposed, and the corresponding simulation tests were carried out. The evolution of Al2Cu second phase particles and the mechanical properties of the produced workpieces were investigated. The results showed that the degree of crushing, dissolution, and precipitation of Al2Cu particles were significantly improved in the improved process, and the area fractions of Al2Cu coarse second phase particles after saddle forging and rolling were significantly reduced, leading to 2.4 times increase in area fraction of the θ′ phase after T8 treatment. More homogeneous slip occurred during the tensile testing process and intergranular fracture was the main fracture mechanism. The tensile strength σb, yield strength σs, and elongation δ in the radial direction of the 2219 workpieces were increased to 491 MPa, 388 MPa, and 13.1%, where were increases of 11%, 14%, and 68%, respectively. The uniformity in σb, σs, and δ of the 2219 workpieces increased by 57%, 38%, and 64%, respectively.

Critical Strain for Dynamic Recrystallisation. The Particular Case of Steels

Abstract: The knowledge of the flow behavior of metallic alloys subjected to hot forming operations has particular interest for metallurgists in the practice of industrial forming processes involving high temperatures (e.g., rolling, forging, and/or extrusion operations). Dynamic recrystallisation (DRX) occurs during high temperature forming over a wide range of metals and alloys, and it is known to be a powerful tool that can be used to control the microstructure and mechanical properties. Therefore, it is important to know, particularly in low stacking fault energy materials, the precise time at which DRX is available to act. Under a constant strain rate condition, and for a given temperature, such a time is defined as a critical strain (ec). Unfortunately, this critical value is not always directly measurable on the flow curve; as a result, different methods have been developed to derive it. Focused on carbon and microalloyed steels subjected to laboratory-scale testing, in the present work, the state of art on the critical strain for the initiation of DRX is reviewed and summarized. A review of the different methods and expressions for assessing the critical strain is also included. The collected data are well suited to feeding constitutive models and computational codes.

Mechanical properties of near alpha titanium alloys for high-temperature applications - a review

Abstract: This paper aims to present a broad review of near-a titanium alloys for high-temperature applications.,Following a brief introduction of titanium (Ti) alloys, this paper considers the near-α group of Ti alloys, which are the most popular high-temperature Ti alloys developed for a high-temperature application, particularly in compressor disc and blades in aero-engines. The paper is relied on literature within the past decade to discuss phase stability and microstructural effect of alloying elements, plastic deformation and reinforcements used in the development of these alloys.,The near-a Ti alloys show high potential for high-temperature applications, and many researchers have explored the incorporation of TiC, TiB SiC, Y2O3, La2O3 and Al2O3 reinforcements for improved mechanical properties. Rolling, extrusion, forging and some severe plastic deformation (SPD) techniques, as well as heat treatment methods, have also been explored extensively. There is, however, a paucity of information on SiC, Y2O3 and carbon nanotube reinforcements and their combinations for improved mechanical properties. Information on some SPD techniques such as cyclic extrusion compression, multiaxial compression/forging and repeated corrugation and straightening for this class of alloys is also limited.,This paper provides a topical, technical insight into developments in near-a Ti alloys using literature from within the past decade. It also outlines the future developments of this class of Ti alloys.

Microstructure-property relationships in directly aged Alloy 718 turbine disks

Abstract: Direct ageing (DA) of forged Alloy 718 turbine disks enables the design of more efficient aircraft engines due to high-temperature yield strength increments of around 10%. This ‘DA effect’ is related to the dislocation density, δ-phase content and nanoscale γ′- and γ"-precipitate morphology. However, in real turbine disks, local differences in the thermo-mechanical history often deteriorate the DA effect below customers specifications. Thus, the aim of this paper is to unravel the complex microstructural evolution in low-versus high-yield strength regions. We use hardness mapping, macro-etching, thermo-kinetic and FEM modelling to identify the regions of interest. EBSD, TEM and atom probe microscopy (APM) enable micro- and nanostructure characterization. Low-hardness regions exhibit larger grains, lower δ-phase contents, and lower geometrically necessary dislocation densities. Nanoscale γ′- and γ"-precipitates are coarser, with lower number density, and more complex coprecipitate morphology. We assign the origins of these changes to local temperature and strain conditions during forging, and inhomogeneities in pre-materials. A proposed microstructural model explains the underlying mechanisms. Local strain-induced δ-phase dissolution results in recovery, recrystallisation and grain growth during forging, reducing the number of nucleation sites for precipitation. Thus, the DA effect deteriorates due to accelerated γ"-precipitate coarsening and less uniform particle dispersions.

The effect of α+ β forging on the mechanical properties and microstructure of binary titanium alloys produced via a cost-effective powder metallurgy route

Abstract: Titanium and its alloys have been studied intensively in the last decades due to their superb mechanical properties; however, the high production costs of titanium and its alloys is considered to be one of the enormous obstacle which limits the use of these outstanding alloys in engineering applications. This study focuses on a cost-effective method of producing Ti-x Cu/Mn alloys (x = 0.5, 2.5 and 5 wt,%/1, 5 and 10 wt% respectively) via the powder metallurgy route. The samples were uniaxially cold pressed and sintered, and then subjected to one-step forging in the α+β field. The effect of the α+β forging on the microstructures and the mechanical properties was investigated, and the relationship between them discussed. It has been found that even with lower forging temperatures (below the β transus), these alloys have similar ultimate tensile strength (647–1035 MPa and 741–1442 MPa respectively) and Vickers hardness (238–315 HV and 234–388 HV respectively) to that of β forged Ti–Cu/Mn alloys.