Search Results (18)

Co-Cr-Mo alloys are in high demand as materials for medical implants. However, hot processing of these alloys is quite difficult due to the need to maintain narrow temperature range of deformation to achieve the required mechanical properties and structure of the products. The features of formation of structure, phase composition and mechanical properties of Co-Cr-Mo alloy at the main stages of thermomechanical treatment were considered in this study. The results demonstrated a significant enhancement in the strength characteristics of the alloy during processing in both forging and radial shear rolling (RSR). At the same time, radial shear rolling processing simultaneously increased the strength and ductility of the alloy. According to the XRD analysis data, the phase composition changes from single-phase structure (FCC-phase) after forging to a mixture of FCC-phase and HCP-phase after RSR during processing. The structure gradient characteristic of RSR decreased as the total elongation ratio increased, maintaining a tendency towards a finer-grained structure near the surface of the bars and a coarser one in the center. This tendency was reflected in the average grain size and the level of mechanical properties. Combined thermomechanical treatment, including the RSR process, made it possible to achieve a unique formation of microstructure and phase composition in the Co-Cr-Mo alloy, ensuring high strength while maintaining ductility. Full article

This work represents a preliminary study of atmospheric plasma-sprayed (APS) Yttria-Stabilized Zirconia (YSZ)-based thermal barrier coatings (TBCs) deposited on forged and additive manufactured (AM) HAYNES^®282^® (H282) superalloy substrates. The effect of different feedstock morphologies and spray gun designs with radial and axial injection on APS-deposited YSZ layer characteristics such as microstructure, porosity content, roughness, etc., has been investigated. The performance of TBCs in terms of thermal cycling fatigue (TCF) lifetime and erosion behaviour were also comprehensively investigated. In view of the high surface roughness of as-built AM surfaces compared to forged substrates, two different types of NiCoCrAlY bond coats were examined: one involved high-velocity air fuel (HVAF) spraying of a finer powder, and the other involved APS deposition of a coarser feedstock. Despite the process and feedstock differences, the above two routes yielded comparable bond coat surface roughness on both types of substrates. Variation in porosity level in the APS topcoat was observed when deposited using different YSZ feedstock powders employing axial or radial injection. However, the resultant TBCs on AM-derived substrates were observed to possess similar microstructures and functional properties as TBCs deposited on reference (forged) substrates for any given YSZ deposition process and feedstock. Full article

With the wide application potential of wrought aluminium alloy in aerospace, automobile and electronic products, high-quality aluminium bars prepared by the radial forging (RF) process have received extensive attention. Penetration performance refers to the depth of radial plastic deformation of forgings, which is the key factor in determining the quality of forging. In this work, the penetration performance of the radial forging process for 6063 wrought aluminium bars is investigated by simulation using FORGE software. The minimum reduction amount of the hammer is calculated based on the forging penetration theory of forging. The influence of process parameters including forging ratio (FR) and billet temperature on the effective stress and hammer load in the RF process are investigated. The RF-deformed billet is then produced with the optimal process parameters obtained from the simulation results. The average grain size of aluminium alloy semi-solid spherical material is used to evaluate the forging penetration. Simulation results showed that the effective strain at the edge and the centre of the RF-deformed billet gradually increases, but the increasing speed of the effective strain at the edge becomes low. The hammer load first decreases quickly and then gradually maintains stability by increasing the FR. It is found that low billet temperature and high FR should be selected as appropriate process parameters under the allowable tonnage range of RF equipment. Under an isothermal temperature of 630 °C and a sustaining time of 10 min, the difference in the average grain dimension between the edge and the centre positions of the starting extruded blank is 186.43 μm, while the difference in the average grain dimension between the edge and the centre positions of the RF-deformed blank is 15.09 μm. The improvement ratio of penetration performance for the RF-deformed blank is obtained as 91.19%. Full article

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. Full article

The rolling process of rings is a commonly used method for producing annular forgings. There are two primary types of this process: radial-axial rolling and radial rolling. This article presents the research results regarding the latter, in which obtaining a product with the assumed dimensions constitutes a major problem. In industrial practice, the process parameters are based on the experience of technologists and/or by trial and error. This is why the authors considered it justified to undertake the research aimed at determining the influence of the main process parameters, that is, preform temperature and tool speed, on the shape and dimensions of the cross-section, which determine the internal and external diameters of the rolled ring. The research was based on numerical simulations and experimental studies. The results obtained proved that the higher the feed speed of the main roll, the greater the change in the cross-sectional height during rolling, and the smaller the cross-sectional deformation (the so-called fishtail). Nevertheless, a higher preform temperature reduces the final height of the ring and reduces cross-section deformation. On the basis of the obtained test results, guidelines for the process design were postulated, considering the influence of temperature and speed parameters on the final dimensions of the forging and the dimensions of the preform. Full article

Low-carbon steel has been popularly applied in numerous applications because of its unique features, such as good plasticity, high strength, great hardness, and excellent toughness. Additionally, the semi-solid thixotropic forging forming method has been widely used in light alloys, due to its advantages of low forming force and high forming quality, whereas its application in ferrous materials is still limited. In this study, the semi-solid thixotropic forging forming process is proposed for producing the low-carbon steel claw pole, with the main stages being radial forging deformation, isothermal treatment, and forging forming. The effect of the area reduction rate on the effective strain from the cross sections of the radial-forged metal bar was studied using numerical simulations. The effect of the isothermal holding process on the microstructures of radial-forged billets was investigated, to obtain the ideal semi-solid microstructures. The microstructure and mechanical properties of low-carbon steel claw poles from the thixotropic forging experiment are presented and discussed. It was found that when the area reduction rate was 67%, the effective strain at the edge of the metal bar exceeded 5.0, while the effective strain at the center was above 1.2, indicating an excellent quality of forging for the bar. The optimization of the process parameters for preparing low-carbon steel semi-solid billets with fine and globular microstructures was achieved with an area reduction rate of 67%, an isothermal temperature of 1500 °C, and a duration time of 15 min. Moreover, the low-carbon steel claw pole fabricated with the optimized operating parameters was found fully filled, with a sharp profile and a flat surface, where the yield strength and tensile strength increased by 88.5% and 79.8%, respectively, compared to the starting materials. Full article

In this study, steel/aluminum bimetal gears were manufactured under different deformation degrees by using hot forging processing. Optical microscope (OM), scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) were used to observe morphologies and the element composition of the interface region of the bimetal gears with different deformation degrees. Results show that the interface region between steel and aluminum is of mechanical bonding characteristics when the deformation degree is 50% and 70%, and the steel–aluminum interface joining zone is of the metallurgical bonding feature when the deformation degree is 90%. Finite element (FE) simulation of the hot forging process of the bimetal gear was carried out by using DEFORM-3D software. The simulation results show that the increase in the difference between the interfacial radial stress and the flow stress of the steel helps to form metallurgical bonding at the steel–aluminum joining zone. Full article

Gradient variations of through-thickness residual stress, microstructure and texture greatly affect the performance of cold radial forged tubes. In this work, the through-thickness distribution of residual stress was measured based on the Debye ring. The microstructure was characterized with the electron backscattering diffraction technique. The texture was measured by the X-ray diffractometer. The influence of microstructure and texture on the strength and anisotropy of forged tubes with different thickness reductions was analyzed. The results show that the residual stress varies gradually from compressive to tensile from the outer to inner surface. The microhardness of the outer surface is lower than the inner. The dislocation density and low-angle grain boundary fraction are the smallest in the one-third thickness. The dislocation density and low-angle grain boundary fraction increase gradually from the one-third thickness to the inner surface. The main texture components of the forged tube include {111}<110>, {001}<110> and {114}<110>. Texture {111}<110> deflects gradually toward {114}<110>, {112}<110> and {110}<110> from the external tube to the internal tube. The gradient variation of strength mainly resulted from the difference of the dislocation density. The difference of strength along the radial direction is reduced with a larger thickness reduction. This work has important significance for improving the performance of high-strength alloy steel tubes processed by cold radial forging. Full article

The hydrogen embrittlement problem of alloy steel heavy forgings not only has the common properties of general hydrogen embrittlement, but also has the characteristics brought by its scale characteristics. The research of hydrogen embrittlement, combined with its characteristics and commonness, is of vital importance for the service safety of engineering structures. The temperature field and microstructure distribution in the machining process were investigated through the simulation of a finite element. On this basis, the physical simulation experiments were carried out to obtain the microstructure of heavy forgings in radial directions. The hydrogen embrittlement sensitivity was characterized by electrochemical hydrogen charging and slow strain rate tests (SSRT). The microstructure and fracture morphology of the samples were characterized to explore the law and mechanism of hydrogen embrittlement sensitivity gradient distribution along the axial direction. It is helpful to understand the hydrogen embrittlement of heavy forgings in order to guide engineering practice. Full article

Powder metallurgy is one way of producing complex, graded structures that could allow material systems to be produced with properties tailored to individual applications. However, powder metallurgy requires that the semi-finished products are very similar to the final component. It is much more economical to produce simple semi-finished products and then combine them by powder forging and simultaneous compaction than forming complex components with the desired graded structure. However, it is absolutely necessary that the graded structure of the semi-finished products is maintained during the forming process. In this study, pre-sintered cylindrical semi-finished products, consisting of axially graded as well as radially graded components, were produced by powder forging at 1100 °C. The microstructures, densities and mechanical properties of the final components were investigated to verify the effectiveness of the process route. It was observed that the components formed solid structures after compaction, in which the reinforcing ZrO₂ particles were fully integrated into the transformation-induced plasticity steel matrix. Full article

Al-Mg-Si based alloys are popular alloys used in the automotive industry. However, limited studies have been performed to investigate the microstructure, deformation characteristics, and deformation mechanism for the semi-solid 6063 alloys. In this study, the cold radial forging method and semi-solid isothermal treatment (SSIT) are proposed in the semi-solid isothermal compression (SSIC) process to fabricate high-quality semi-solid 6063 billets. The effects of deformation temperature, strain rate, and strain on the microstructure, deformation characteristics, and deformation mechanism of the SSIC of cold radial forged 6063 alloys were investigated experimentally. Constitutive equations were established based on the measured data in experiments to predict the flow stress. Results show that an average grain size in the range from 59.22 to 73.02 μm and an average shape factor in the range from 071 to 078 can be obtained in the microstructure after the cold radial forged 6063 alloys were treated with SSIT process. Four stages (i.e., sharp increase, decrease, steady state, and slow increase) were observed in the true stress- true strain curve. The correlation coefficient of the constitutive equation was obtained as 0.9796 while the average relative error was 5.01%. The deformation mechanism for SSIC of cold radial forged aluminum alloy 6063 mainly included four modes: The liquid phase flow, grain slide or grain rotation along with the liquid film, slide among solid grains, and the plastic deformation of solid grains. Full article

Radial forging is a reliable way to produce Ti alloy rods without preliminary mechanical processing of their surface, which is in turn a mandatory procedure during almost each stage of the existing technology. In the present research, hot pressing and radial forging (RF) of the titanium-based Ti-3.3Al-5Mo-5V alloy were carried out to study the specifics of plasticized metal flow and microstructural evolution in different sections of the rods. The structural analysis of these rods was performed using metallography and X-ray diffraction techniques. The X-ray diffraction reveals the two-phase state of the alloy. The phase content in the alloy was shown to vary upon radial forging. Finally, radial forging was found to be a reliable method to achieve the uniform fine-grained structure and high quality of the rod surface. Full article

Dense β-SiC coating with 3C-structure was utilized as a dry cold forging punch and core-die. Pure titanium T328H wires of industrial grade II were employed as a work material. No adhesion or galling of metallic titanium was detected on the contact interface between this β-SiC die and titanium work, even after this continuous forging process, up to a reduction in thickness by 70%. SEM (Scanning Electron Microscopy) and EDX (Electron Dispersive X-ray spectroscopy) were utilized to analyze this contact interface. A very thin titanium oxide layer was in situ formed in the radial direction from the center of the contact interface. Isolated carbon from β-SiC agglomerated and distributed in dots at the center of the initial contact interface. Raman spectroscopy was utilized, yielding the discovery that this carbon is unbound as a free carbon or not bound in SiC or TiC and that intermediate titanium oxides are formed with TiO₂ as a tribofilm. Full article

The α and prior β textures and microtextures of a lamellar Ti6242 forged disk were characterized by advanced electron back scattered diffraction (EBSD) and related to crystallographic features of faceted crack initiation sites of dwell fatigue specimens tested along the radial direction (RD). Large feather-like structures of α colonies with close orientations were observed at boundaries of elongated prior β grains. Their orientation belongs to the <11-20>α//z fiber, aligning the c-axis in RDs (z: axial direction of the disk). They are inherited from prior β grains belonging to the major <100>β and minor <111>β//z fibers. These feather-like structures are strong regions of the forging that act as a preferential crack initiation site. Adjacent to them, one can observe large colony with evidence of prismatic slip. Thus, the facet formation seems triggered by stress redistribution from “weak” to “strong” regions due to the elastic and plastic anisotropy. Finally, the occurrence of neighboring β grains able to share close oriented feather-like colonies is discussed considering the reconstructed β microtexture and texture. This study may be helpful for further texture control during the forging process. Full article

The article presents the influence of structure formation on the properties of 321 metastable austenitic stainless steel in the process of cold radial forging (CRF). The steel under study after austenitization was subjected to CRF at room temperature with degrees of true strain (e) 0.26, 0.56, 1.00, 1.71 and 2.14. It has been shown that structure formation of the studied steel during CRF consists of three stages: formation of the lamellar structure of austenite, formation of the trapezoidal structure, and formation of the equiaxial grain structure. The kinetics of the strain-induced α′-martensitic transformation is related to the stages of structure evolution. Hardness, ultimate tensile strength and yield strength uniformly increase in all stages of structure formation with a significant decrease of elongation to fracture during the first stage of structure formation while the value of elongation to fracture remains constant in the subsequent stages of deformation. Impact strength of fatigue cracked specimens (KCT) decreases sharply at the first stage of structure formation and smoothly increases at the second and third stages. However, the impact strength of V-notch specimens (KCV) continuously decreases when deformation degree increases in the overall investigated deformation range. Full article