Transparent polycrystalline magnesium aluminate spinel (PMAS), owing to its high optical transparency with acceptable mechanical properties and chemical stabilities, exhibits great potential for ...optical applications under extreme environments and operating conditions. The first stage of preparing highly transparent PMAS is attainable with the rapidly maturing sintering technology. However, the machining technologies aiming to achieve high shape accuracy and surface quality on PMAS are still restricted by its poor machinability and limited endeavours to survey. This paper provides a comprehensive collection of PMAS processing strategies. The state-of-the-art techniques for sintering PMAS are reviewed with a focus on the technical details and intimate relationship with the material properties. The fundamental material properties of PMAS including the crystal structure, mechanical properties and damage mechanisms are systematically discussed. These characteristics inherently govern the material removal mechanisms and the generation of surface damages in the subsequent machining processes. The surveyed fundamental studies signify that the combination of high brittleness, strong anisotropy within each single-crystal grain and polycrystalline structure is the major obstacle in achieving damage-free surface finish. In this regard, further explorations of improving machining performance with advanced machining technologies and enhancing the machinability through optimising sintering strategies are expected in the outlook.
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•Progression and advancements for PMAS are comprehensively reviewed from synthesis to machining in the processing chain.•The spinel sintering methods are systematically classified with its parameters governing the material properties outlined.•Unique mechanical properties and poor machinability of spinel brought by its intrinsic crystal structure are highlighted.•Current efforts to study the material removal mechanism and machining technologies of spinel are critically summarised.•Outlooks are outlined to improve the spinel processability in conjunction with its sintering strategy optimisation.
High-entropy alloy (HEA) is an emerging alloy which consists of five or more metallic elements with equimolar concentrations and exhibits excellent mechanical properties at cryogenic temperature. ...However, its machinability is almost unknown. In this study, high frequency one-dimensional ultrasonic vibration-assisted diamond turning (UVDT) experiments were conducted on an FeCrCoMnNi-based HEA to investigate the micro-nanoscale material removal mechanisms. Compared with conventional diamond turning, UVDT produced thinner chips, lower cutting forces, less tool wear and better surface integrity. Due to the ultrasonic vibration-assisted burnishing effect, surface scratches were significantly eliminated. A freeform surface was test-fabricated with optical-level finish.
Interest in natural fiber–reinforced composites (NFRCs) is increasing rapidly thanks to their numerous advantages such as low cost, biodegradability, eco-friendly nature, relatively good mechanical ...properties, and a growing emphasis on the environmental and sustainability aspects of engineering materials. However, large-scale use of NFRCs is still considered as challenging due to the difficulties in manufacturing, limited knowledge of its machinability and appropriate parameter settings, and being prone to machining-induced defects. This article presents a comprehensive review on various aspects of NFRCs, with a focus on the manufacturing and machinability. It covers some recent works related to NFRCs, including the manufacturing processes and parameters, characterization of mechanical properties, applications, and machinability and machining process monitoring, many for the first time. The main challenges associated with machining of NFRCs and the induced damages are outlined, with special attention paid to the effect of physical properties of the fibers and manufacturing process on the machinability, along with the essential machining parameters that affect the quality of the machined surface. The research perspectives and the current application status are also discussed. The article is intended to help readers attain a fundamental understanding of key technologies and the state of the arts in this research area.
To improve microhardness and tribological properties of IN718, WC-12Co particles were added to it by the laser cladding. This study investigated the effect of the content of WC-12Co on the ...microstructure, phase composition, microhardness, tribological properties and machinability of the composite coating. The results shows that WC-12Co can inhibit the growth of columnar grains and the (200) growth direction of γ-Ni, and refine the microstructure. The average microhardness of coating increases from 245.83HV0.5 to 462.63HV0.5 with the increase of WC-12Co content. The coating containing 30% wt. WC-12Co has the smallest wear loss, that is, the best wear resistance. However, the coating containing 20 wt% WC-12Co has the lowest COF (0.518), that is, the best antifriction capability. With the increase of WC-12Co content, the milling force increases and the instability of the cutting process is aggravated. Moreover, with the addition of WC-12Co, the wear mechanism changed from adhesive wear to abrasive wear and oxidation wear.
In recent years, additive manufacturing (AM) of metallic parts opens new opportunities for many critical industrial sectors and individual necessities. The high quality and more functional components ...which are difficult or impossible to produce with the conventional methods can be readily manufactured using AM. In addition, minimization of design constraints, minimal material usage and elimination of tooling costs are some of the other notable advantages of this technology. However, poor surface quality of the produced parts is an inherent output of AM. Surface quality has an important effect on the functional performances of the machinery components. Therefore, additional machining operations are usually needed for the AM components to ensure desired part performance. In this context, it is critical to determine machinability and part quality of AM components since they can exhibit different mechanical, physical, and microstructural properties when compared to conventionally manufactured equivalents. In this review article, machinability of 3D printed metallic parts fabricated by Selective Laser Melting (SLM) and Electron Beam Melting (EBM) technologies was investigated. For that purpose, turning, milling, drilling, and micro machining performances of SLM and EBM parts were evaluated considering surface integrity, tool wear, tool life, cutting forces and chip formation depending on the different cutting conditions, 3D printing parameters, building directions, and post-process heat treatments. In addition, some mechanical and physical properties, and microstructural properties of metallic SLM and EBM parts were also introduced from a machinability point of view. The main objective of this paper is to compile relevant information about the conventional and micro machinability performances of 3D printed metallic materials fabricated by SLM and EBM into a single document and to give some suggestions about machining strategies of these novel engineering materials. In addition, the possible perspectives of future studies for enhancement of machinability and surface integrity of AM components are also introduced.
This study examined the hard turning of AISI D2 cold work tool steel subjected to deep cryogenic processing and tempering and investigated the effects on surface roughness and tool wear. In addition, ...the effects of the deep cryogenic processes on mechanical properties (macro and micro hardness) and microstructure were investigated. Three groups of test samples were evaluated: conventional heat treatment (CHT), deep cryogenic treatment (DCT-36) and deep cryogenic treatment with tempering (DCTT-36). The samples in the first group were subjected to only CHT to 62 HRc hardness. The second group (DCT-36) underwent processing for 36h at −145°C after conventional heat treatment. The latter group (DCTT-36) had been subjected to both conventional heat treatment and deep cryogenic treatment followed by 2h of tempering at 200°C. In the experiments, Al2O3 + TiC matrix-based untreated mixed alumina ceramic (AB30) and Al2O3 + TiC matrix-based TiN-coated ceramic (AB2010) cutting tools were used. The artificial intelligence method known as artificial neural networks (ANNs) was used to estimate the surface roughness based on cutting speed, cutting tool, workpiece, depth of cut and feed rate. For the artificial neural network modeling, the standard back-propagation algorithm was found to be the optimum choice for training the model. Three different cutting speeds (50, 100 and 150m/min), three different feed rates (0.08, 0.16 and 0.24mm/rev) and three different cutting depths (0.25, 0.50 and 0.75mm) were selected. Tool wear experiments were carried out at a cutting speed of 150m/min, a feed rate of 0.08mm/rev and a cutting depth of 0.6mm. As a result of the experiments, the best results for both surface roughness and tool wear were obtained with the DCTT-36 sample. When cutting tools were compared, the best results for surface roughness and tool wear were obtained with the coated ceramic tool (AB2010). The macroscopic and micro hardness values were highest for the DCT-36. From the microstructural point of view, the DCTT-36 sample showed the best results with homogeneous and thinner secondary carbide formations.
Additive manufacturing (AM) is characterised by several unique advantages, such as (freedom of) design, capability of fusing dissimilar materials, near-net-shape, and achieving a more sustainable ...production. While the increased precision of metal AM in recent years reduced the needed amount of post-processing to meet dimensional tolerance, the requirements for functional surfaces necessitate a well-understood post-processing, ranging from heat treatment to machining and finishing. The inherently rough initial (as-built) surface topography next to complex material microstructure affects the capability of post-processing/finishing operations to smooth the surface texture and obtain a favourable surface integrity. In this respect, a more fundamental understanding of the effects of material properties on post-processing/finishing is needed. Therefore, this review paper aims to establish the relationship between the characteristics of different AM technologies, microstructural properties of materials in as-built and heat-treated conditions, and the physical properties influencing the response of additively manufactured materials during post-processing/finishing operations. In particular, emphasis is placed on the physics-based understanding of how the microstructural characteristics of 316L, Ti6Al4V and Alloy 718 produced using the two principal technologies, Powder Bed Fusion (PBF) and Direct Energy Deposition (DED), influence their mechanical properties like tensile strengths, hardness and ductility. These properties are among the key factors influencing the response of material during post-processing/finishing operations involving material removal by shear deformation. This review paper also discusses the role of post-processing/finishing on fatigue performance, tribological behaviour and corrosion resistance of investigated AM materials. The paper summarises the state-of the art of post-processing/finishing operations and future research trends are highlighted.
The influence of Si and Al additions to 0.55 mass% C steel on machinability is discussed in cutting with a fly tool of TiAlN coated high speed steel, as performed in gear cutting. Three model steels ...are prepared with controlling nearly the same hardness to study the effects of the alloying elements: one reference steel with C as the only alloying element (Base steel), and two steels alloyed also with 1 mass% Si or Al. The cutting tests are performed to obtain the cutting forces, observe the cutting chips and analyze the damage on the rake faces of the tools. The orthogonal cutting data in the cutting force simulation are identified to minimize the discrepancies between the measured and the simulated forces for the tested steels. When cutting the Base steel, few adhered materials form and the coated thin layer is worn mainly by abrasion. When cutting the Si alloyed steel, the coating surface is covered by adhered layers containing Si–O, Fe2SiO4 and FeO, which contribute to the lowest friction and protect the coated thin layer from wear. When cutting the Al alloyed steel, an Al2O3 layer forms on the coating. The Al2O3 layer induces high friction, large cutting forces and cutting heat, resulting in the rapid substrate softening and coating fracture.
In the first part of this two-part comprehensive study, mechanical properties and machinability characteristic of filament wound hybrid composite pipes with various stacking sequences of glass and ...carbon fibers (Glass-Carbon-Glass (GCG), Carbon-Glass-Glass (CGG), and Glass-Glass-Carbon (GGC)) were investigated experimentally. In order to determine the mechanical properties of the pipes, hardness test (Shore D), ring tensile test (ASTM D2290), and burst test (ASTM D1599) were carried out. Machinability tests were performed at various feed rates (50, 150, 250 and 350 mm/min) and spindle speeds (796, 1592, 2388 and 3184 rpm) using with and without a back-up. The results showed that stacking of the carbon layer between two glass layers (GCG) presented better performance in terms of mechanical properties and machinability characteristic. The maximum ring tensile stress of GCG specimen is 27% and 19% higher than those of GGC and CGG specimens, respectively. On the other hand, the lowest thrust forces measured during the drilling of GCG specimen while the GGC represented highest values. In addition, the use of back-up led to an increase in thrust force. The highest increase was observed in GGC sample. In GGC sample, a change in a spindle speed increased thrust force by 18–35%, while a change in feed rate increased thrust force by 20–30%.
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