Aerospace Components Research Articles

Improvement in Corrosion Performance of ECAPed AZ80/91 Mg Alloys Using SS316 HVOF Coating.

Mg AZ80/91 alloys are highly popular due to their lightweight, high strength-to-weight ratio, and good machinability. However, their moderate mechanical properties and corrosion resistance have limited their use in the automotive, aerospace, and defense sectors. This study primarily aims to enhance the mechanical performance and corrosion resistance of Mg AZ80/91 alloys, making them more suitable for applications in the aerospace and automotive industries. Firstly, equal-channel angular pressing (ECAP) of Mg AZ80/91 alloys has been attempted to improve their mechanical properties. Secondly, a high-velocity oxy-fuel (HVOF) coating of SS316 was applied over the Mg AZ80/91 substrate to enhance its corrosion resistance. In the second step, an HVOF coating of SS316 is applied over the Mg AZ80/91 substrate for better corrosion resistance. The experimental findings demonstrate that the application of an SS316 coating on the ECAP-4P AZ80/91 Mg alloy substrate results in a uniform and dense layer with an average thickness of approximately 80 ± 5 µm. The HVOF-based SS316 coating on 4P-ECAP leads to a noteworthy enhancement in microhardness and a reduction in the corrosion rate, especially in a NaCl solution (3.5 wt.%). This improvement holds great promise for producing reliable, long-lasting, and resilient automotive, aerospace, and defense components. The application of an HVOF-based SS316 coating onto the AZ80 Mg alloy, which had not undergone ECAP treatment, led to a substantial enhancement in corrosion resistance. This resulted in a notable decrease in the corrosion current density, reducing it from 0.297 mA/cm2 to 0.10 µA/cm2.

Creep rupture life prediction of high-temperature titanium alloy using cross-material transfer learning

High-temperature titanium alloys are the key materials for the components in aerospace and their service life depends largely on creep deformation-induced failure. However, the prediction of creep rupture life remains a challenge due to the lack of available data with well-characterized target property. Here, we proposed two cross-materials transfer learning (TL) strategies to improve the prediction of creep rupture life of high-temperature titanium alloys. Both strategies effectively utilized the knowledge or information encoded in the large dataset (753 samples) of Fe-base, Ni-base, and Co-base superalloys to enhance the surrogate model for small dataset (88 samples) of high-temperature titanium alloys. The first strategy transferred the parameters of the convolutional neural network while the second strategy fused the two datasets. The performances of the TL models were demonstrated on different test datasets with varying sizes outside the training dataset. Our TL models improved the predictions greatly compared to the models obtained by straightly applying five commonly employed algorithms on high-temperature titanium alloys. This work may stimulate the use of TL-based models to accurately predict the service properties of structural materials where the available data is small and sparse.

Microstructure and mechanical properties of hybrid nano-titanium carbide-carbon nanotubes (nano-TiC-CNT) reinforced aluminium matrix composite

To use Al composites in structural applications, we need to improve strength and ductility at the same time. In this article, we explore three main concepts to solve this problem: improving the dispersion uniformity of CNTs in Al powder without damaging its structure by solution coating technique, fabricating a hybrid composite by reinforcing Al with nano-TiC-CNT, comparing the properties of nano-TiC-CNT and micron-TiC-CNT hybrid composites. Microstructure observation by SEM, TEM, and XRD revealed well-dispersed and preserved CNTs without the formation of a second phase. The Al-0.5CNT composite showed good tensile strength and elongation at break of 278 MPa and 14%, respectively. Further improvements in tensile strength and ductility of 285 MPa and 23%, respectively, were measured after the addition of 2.5 wt%; (1.4 vol%) TiC nanoparticles to Al-0.5CNT composite. However, the introduction of 2.5 wt-% TiC macroparticles only improved the tensile strength by 48% but elongation at break was up to 32%. The improved strength and ductility are attributed to the introduction of geometrical necessary dislocation and Orowan looping of dislocations leading to back stress strengthening. The new Al composite is expected to find application in automotive and aerospace component manufacture and thermal management.

Virtual source total focusing method for crack detection in complex curved structure

Accurate non-destructive testing and evaluation of cracks is important for the quality assurance and life-cycle management of key components in aerospace and energy industries. This paper presents a novel imaging method for cracks detection in complex curved structure , combining virtual source technique, multi-mode total focusing method and phase coherence imaging method. The virtual source on the sample surface is employed as the emitter and receiver for the ultrasonic array imaging. In this way, the calculation complexity of imaging algorithm due to beam path search can be reduced, and the detection sensitivity in the region of interest can be improved. In addition, the phase coherence factor is used to suppress the background noise and imaging artifacts, which significantly improves the quality of ultrasonic array imaging. A complex curved sample with variable thickness and non-developable surface was used to examine the effectiveness of the virtual source total focusing method. The signal-to-noise ratio of the crack defect is increased by more than 25 dB using the novel method compared with that of the conventional total focusing method, and the quantitative evaluation error of defect is less than 2.67%.

Intelligent Additive Manufacturing Architecture for Enhancing Uniformity of Surface Roughness and Mechanical Properties of Laser Powder Bed Fusion Components

In the Laser Powder Bed Fusion (L-PBF) process, 3D components with complex geometries are fabricated in a layer-by-layer fashion by using a controlled laser beam to selectively melt particular regions of the metal powder bed. However, due to the stochastic nature of the L-PBF process, the top surface roughness of each solidified layer tends to be different even when the optimal processing conditions for the different positions on the build plate are employed. As a result, the mechanical properties of the built components frequently vary from one component to the next. Accordingly, this study proposes an Intelligent Additive Manufacturing Architecture (IAMA) for controlling the surface roughness of each build layer through an appropriate adjustment of the laser re-melting parameters. The IAMA architecture comprises five modules, namely In-Situ Metrology (ISM), Ex-Situ Metrology (ESM), Automatic Virtual Metrology (AVM), Additive Manufacturing Simulation (AMS) and Intelligent Compensator (IC). The feasibility of the proposed architecture is demonstrated by comparing the top surface roughness of cubic and mechanical strengths of tensile test samples built using the proposed method with those built using a traditional L-PBF approach without surface roughness control. It is found that the samples fabricated using the IAMA approach have an average top surface roughness of 1.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m and a standard deviation is 0.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m. By contrast, the samples produced using the traditional L-PBF approach have an average surface roughness of 13.45 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m and a standard deviation of 2.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m. In addition, the specimens produced with the assistance of IAMA architecture have an average tensile strength of 1013 MPa with a standard deviation of 69.5 MPa, while those printed without surface roughness control have an average tensile strength of 903 MPa with a standard deviation of 101.4 MPa <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —As L-PBF produce part in a layer-by-layer manner, therefore, the roughness on the top surface of previous layer have a strong influence on the printing quality of current layer. The variations of surface roughness will lead to the fluctuation of mechanical properties of the fabricated components. Additionally, to the best of author’s knowledge, current commercial L-PBF machines can not actively control the surface roughness of samples during the process. The proposed IAMA in this work can predict and control the roughness on the top surface of each layer during L-PBF process. Therefore, the constructed architecture has strong potential for integrating into the commercial L-PBF machine for controlling the surface roughness on the top of the parts during the manufacturing process. As a result, the quality of the fabricated components is expected to be in consistent. Accordingly, L-PBF machine equipped with IAMA will have a strong potential in applying for mass production of the components in aerospace and automobile industries.

Biopolymer-coated composites for enhanced dielectric and electromagnetic interference shielding applications - a green initiative

The utilization of natural fibre-reinforced polymer composites has been tremendously growing in various applications of automotive and aerospace components. In this aspect, the researcher’s community is approaching the global market with new ideas for developing a complete eco-friendly, sustainable, and green composite. Plant-based composites have received great interest from the initial stage due to their unique features, such as lightweight, corrosion resistance, specific properties, excellent mechanical and thermal properties. This research article attempts a novel technique of coating the fibres with polylactic acid (PLA) as a part of surface modification which improves fibre properties. Then the fibres were reinforced with various weight percentages of conductive fillers, such as Copper (Cu), Alumina (Al2O3), and Graphene (Gr), to improve the electrical properties using the hand layup technique. Then the fabricated samples were tested for dielectric and electromagnetic interference (EMI) shielding effectiveness (SE) using resonance and open shielded method. Based on the test results, it was noted that the dielectric strength (K) and shielding effectiveness (SE) of the composites started to increase with the increase of weight percentage of conductive fillers, which highlighted that by incorporating conductive fillers, the fibres started losing their insulation properties. The composites with 0.9 wt% of nanofillers achieved maximum SEabs of −19.61 dB and a SEtotal of −22.67 dB at a frequency range of 8–12 GHz.

The Current State of the Art and Advancements, Challenges, and Future of Additive Manufacturing in Aerospace Applications

Additive manufacturing has revolutionized the manufacturing industry, particularly in aerospace. This paper provides an overview of the advancements, state-of-the-art, challenges, and future of additive manufacturing in the aerospace industry. It begins by discussing the workflow of additive manufacturing and the comparison of software required for modeling and slicing the designed models. Various types of additive manufacturing processes used in the aerospace industry with their postprocessing challenges and solutions are also presented in detail. Besides, the challenges and limitations that come with the use of additive manufacturing in aerospace are also outlined. The paper investigated that the use of additive manufacturing in aerospace has given several advantages such as the ability to produce complex geometries, reduce material waste, and improve design flexibility. The future of additive manufacturing in aerospace looks promising, with the potential for even more cost-effective and efficient production. The paper concludes that additive manufacturing has proven to be a game-changer in aerospace presenting different advanced aerospace components in detail, with continued research and development shaping the future of manufacturing and production. With advancements in technology and processes, additive manufacturing for aerospace can overcome the challenges and become a reliable and cost-effective alternative to traditional manufacturing methods.

A systematic review on high cycle and very high cycle fatigue behavior of laser powder bed fused (L-PBF) Al-Si alloys

The recent attention towards additive manufacturing (AM) of metallic alloys, particularly Al-Si alloys, has been significant due to its important role in the design and development of complex structural components in aerospace, defense, and automotive industries. The use of AM technology, specifically Laser powder bed fusion (L-PBF), enables the creation of lightweight structures with flexible geometries that were previously not achievable through conventional manufacturing methods. Al-Si components fabricated through L-PBF are often subjected to long periods of loading in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) conditions. Therefore, it would be extremely important to investigate fatigue characteristics of these components under both HCF and VHCF regimes. However, it is important to recognize that the fatigue performance of L-PBF Al-Si alloys in HCF and VHCF regimes is not fully understood due to the complex nature of fatigue responses in these regimes. Various factors such as microstructures, defects, porosity, and processing parameters, can potentially influence the fatigue behavior in these regimes, further complicating the analysis. Therefore, optimizing process parameters and post-treatments is essential to achieve the optimal fatigue performance for load-bearing components in both HCF and VHCF conditions. In the past few years, several studies have been conducted to investigate the effect of critical parameters on the fatigue performance of L-PBF Al-Si parts in HCF and VHCF regimes. This article aims to provide a comprehensive and in-depth analysis of recent research findings regarding important factors such as residual stress, surface roughness, build parameters (e.g. build orientation), microstructural characteristics, post-processing methods, manufacturing flaws, specimen shapes, load ratios. These factors can have a significant impact on fatigue properties of L-PBF Al-Si alloys, particularly in the HCF and VHCF ranges. In order to realize the full potential of the L-PBF Al-Si alloys in the development of advanced structural components, this study primarily focuses on identifying key areas that require attention.

A Machine Learning Approach for Segmentation and Characterization of Microtextured Regions in a Near-α Titanium Alloy

The development of automated segmentation and quantitative characterization of microtextured regions (MTRs) from the complex heterogeneous microstructures is urgently needed, since MTRs have been proven to be the critical issue that dominates the dwell-fatigue performance of aerospace components. In addition, MTRs in Ti alloys have similarities to microstructures encountered in other materials, including minerals and biomaterials. Meanwhile, machine learning (ML) offers new opportunities. This paper addresses segmentation and quantitative characterization of MTRs, where an ML approach, the Gaussian mixture models (GMMs) coupled with density-based spatial clustering of applications with noise (DBSCAN) clustering algorithms, was employed in order to process the orientation data acquired via EBSD in the Matlab environment. Pixels with orientation information acquired through electron backscatter diffraction (EBSD) are divided and colored into several “classes” (MTRs) within the defined c-axis misorientations (i.e., 25°, 20°, 15°, 10°, and 5°), the precision and efficacy of which are verified by the morphology and pole figure of the segmented MTR. An appropriate range of c-axis misorientations for MTR segmentation was derived, i.e., 15~20°. The contribution of this innovative technique is compared with previous studies. At the same time, the MTRs were statistically characterized in the global region.

Thermal shock resistant 3D printed ceramics reinforced with MgAl2O4 shell structure

The demand for the swirl nozzle with enhanced temperature resistance and lightweight properties is increasing as the thrust-to-weight ratio of aero-engines rises. The Al2O3 ceramic swirl nozzle can maintain high strength in a hostile environment of high temperature and severe corrosion, while also meeting the requirements of aircraft to enhance efficiency and decrease weight. However, Al2O3 ceramics are limited in their application for aerospace components due to their poor thermal shock resistance (TSR) stemming from their inherent brittleness. This work reported an innovative design and fabrication strategy based on photopolymerization 3D printing technology to realize the three-dimensional shell structure through element interdiffusion and nanoscale stacking of the reinforced phase. With this strategy, a novel type of the new dual-structure Al2O3 ceramic composed of MgAl2O4 shell structure and matrix could be constructed in situ. The nano-sized MgAl2O4 caused a crack passivation effect after the thermal shock, which could improve the strength and TSR of 3D-printed Al2O3 ceramic. In addition, the effects of MgO content and sintering temperature on sintering behavior, flexural strength, porosity, and TSR of Al2O3 ceramics manufactured by digital light processing (DLP) processing were systematically studied. The optimum overall performance of Al2O3 ceramics was obtained at the sintering temperature of 1550 °C and the MgO content of 1.0 wt.%, with a maximum flexural strength of 111.929 MPa and a critical temperature difference of 374.24 °C for TSR. Based on the above research, an aero-engine swirl nozzle with high thermal shock resistance has been successfully prepared by ceramic 3D printing technology, which enhances high-temperature resistance and promotes lightweight design in aero-engine.

Microstructure evolution and ablation mechanism of SiCf/SiC ceramic matrix composite microgrooves processed by pico-second laser

SiCf/SiC ceramic matrix composites have been widely applied in turbine engine aerospace components with high temperature resistance, high strength, and lightweight performances. Due to the high brittleness and anisotropy, laser-assisted machining acts as a feasible process to improve the machinability of the SiCf/SiC composites. A single-factor experiment was designed to understand the microstructure evolution and ablation behaviors of the microgrooves processed by pico-second laser in this study. The high pulse energy/scanning time and low scanning speed had positive impacts on the depth and width, but negative effect on the three-dimensional surface roughness Sa. Besides, the optimal parameter was 200 kHz repetition frequency. In addition, the microstructure evolution and ablation mechanism under different laser parameters were investigated by the HRSEM, EDS, and XRD analysis. These experimental results showed that the machined microgrooves were covered by a large amount flocculent composed of amorphous SiO2 when the oxidation was weak, and the splashes with the form of amorphous SiO2 and crystal SiO2 under strong ablation conditions. This indicated that the plasma effect transformed to the photothermal effect with enough heat. Meanwhile, a condensate layer occurred in all experiments and a recrystallized SiC layer relied on the microgroove depth controlled by adjusting laser parameters. This work will provide a theoretical basis and practice guidance for laser-assisted machining of the SiCf/SiC composites.

Prediction Model for the Evolution of Residual Stresses and Machining Deformation of Uneven Milling Plate Blanks.

During aerospace thin-walled component processing, the prediction and control of machining deformation have gained increasing attention. The initial residual stress in the blank is a major factor leading to the occurrence of machining deformation. This paper proposes the concept of uneven milling during the workpiece machining process, which is caused by the variation in local cutting depth resulting in uneven material removal thickness. Based on the elasticity theory, an analytical model is established to predict the evolution of overall residual stress and machining deformation in beam-like aluminum alloy components under uneven milling conditions. The effectiveness of the model is verified through finite element simulations and experiments. The results are as follows: (1) Under uneven milling conditions, the analytical model can accurately predict the distribution of residual stress and the machining deformation within the ZX section of the workpiece. (2) The uneven distribution of bending stress arises from the different curvature radii of various positions after workpiece deformation, leading to a 1 MPa to 3 MPa difference in stress between the middle and both ends of the workpiece. (3) During the layer-by-layer milling process, the magnitude of workpiece deformation is related to the stress state of the material removed, and there is a deformation superposition effect on the lower surface of the workpiece, further exacerbating the overall machining deformation.

A Comprehensive Review of Aluminium Matrix Composite Reinforced with hBN Particulates

Aluminum alloys are widely employed due to their advantageous combination of properties, including light weight, corrosion resistance, and mechanical strength. These alloys consist predominantly of aluminum with small additions of other elements aimed at enhancing specific characteristics. Ceramic reinforcements like hBN, SiC, Al2O3, and B4C are added to aluminum alloys to make better their mechanical and wear resistance properties. This practice is frequent and enhances the overall performance of the resulting composite materials. The addition of ceramic reinforcements, incorporated into an aluminum matrix, leads to improved strength and stiffness of the composite. This aspect is particularly advantageous in scenarios necessitating high mechanical strength, such as aerospace and automotive components. The review focuses on the effects of hexagonal boron nitride (hBN) reinforcement on composite materials, particularly aluminum alloys. It emphasizes that the properties of these composites can vary based on several factors, including particle size, weight percentage of hBN, and the processing techniques used. The key points addressed in the study include the impact of hBN reinforcement on mechanical behavior (strength and micro-hardness) and wear resistance behavior of the resulting aluminum alloy composites.

An Study Regarding a New Concept of 3D Printing Using a 6 Axis Industrial Robotic ARM

Abstract This paper focuses on a topic that is frequently used nowadays namely 3D printing. The term 3D printing encompasses several manufacturing technologies that build parts layer-by-layer an inconvenience of this process is that the deposition of material takes place in the plane (2D space) then by applying a constant increment on the third axis it is moved to the next plane. The deposition of material is taking part in a 2D space. There are many types of 3D printing such as FDM (fused deposition modeling), SLA (stereolitography), SLS (selective laser sintering), DMLS (direct metal laser sintering), DLP (digital light process), EBM (electron beam melting). Typically these applications involve low-volumes and complex geometries. Often, components for aerospace and medical applications are ideal candidates for production 3D printing. This paper proposes a new approach to the 3d printing process by using a robotic arm to ensure more than 3 degrees of freedom and deposition paths with spatial orientation. One propose two types of working: nonplanar with the tip normal to the working plane and nonplanar with the tip normal to the trajectory.

Deformation and fracture mechanisms of Ti-55531 alloy with a bimodal microstructure under the pre-tension plus torsion composite loading

The deformation and fracture behavior of the Ti-55531 alloy with a bimodal microstructure (BM) under the pre-tension plus torsion composite loading were systematically investigated at room temperature. The results indicate that the pre-tension loading dramatically reduces the subsequent torsional strength of the alloy, while its torsional plasticity is almost not affected. A (101¯0) prismatic slip is initiated inside the primary equiaxed α (αp) phase during the pre-tension stage. Subsequently, several dislocation jogs form inside the αp particles due to the crossing of the (0002)[1¯ 2 1¯ 0] basal and (11¯01) [1¯ 2 1¯ 0] pyramidal slip systems during the torsion deformation stage, which may be a novel deformation mechanism of the Ti-55531 alloy. Moreover, the αp particles are cut by numerous parallel slip bands, resulting in ladder-like structures be formed at the αp/βtrans (β transformed microstructure) interface, which can promote microcrack initiation at the αp/βtrans interfaces. Furthermore, {101¯1}α deformation twins are only detected inside secondary α (αs) phase just during the subsequent torsion deformation stage. In the main bearing phase, the αp particles elongate along specific directions in different deformation regions due to a change in the maximum shear stress. Thus, the cross-section profile from the surface to the center of the specimens after the pre-tension plus torsion deformation can be divided into three regions: torsion, tension plus torsion, and tension deformation regions. These findings can provide a theoretical basis for understanding the deformation damage of aerospace components under complex loads and optimizing their structural design.

Analysis of Cracks in Solution-Treated AISI 17-4PH Stainless Steel Observed During Machining of Aerospace Component

Analysis of Cracks in Solution-Treated AISI 17-4PH Stainless Steel Observed During Machining of Aerospace Component

Characterization of Al-12Si Thin-Wall Properties Fabricated with Laser Direct Energy Deposition

Additive manufacturing is an emerging process that is used to manufacture industrial parts layer by layer and can produce a wide range of geometries for various applications. AM parts are adopted for aerospace, automobiles, antennas, gyroscopes, and waveguides in electronics. However, there are several challenges existing in manufacturing Al components using the AM process, and their mechanical and microstructural properties are not yet fully validated. In the present study, a gas-atomised powder of a eutectic Al-12Si alloy was used as feedstock for the Laser Direct Energy Deposition (LDED) process. A SEM analysis of Al-12Si powder used for processing illustrated that particles possess appropriate morphology for LDED. A numerical control system was used to actuate the deposition head towards printing positions. The deposited samples revealed the presence of Al-rich and Al-Si eutectic regions. The porosity content in the samples was found to be around 2.6%. Surface profile roughness measurements and a microstructural analysis of the samples were also performed to assess the fabricated sample in terms of the roughness, porosity, and distribution of Al and Al/Si eutectic phases. The tensile properties of fabricated thin walls were better compared to casted Al alloys due to the uniform distribution of Si in each layer. Micro-hardness tests on the deposited samples showed a hardness of 95 HV, which is equivalent to casted and powder bed fusion melting samples. The gas atomised Al-12Si powders are highly reflective to a laser and also quick oxidation takes place, which causes defects, porosity, and the balling effect during fabrication. The results can be used as a base guide for the further fabrication of aerospace component design with high structural integrity.

NUMERICAL INVESTIGATIONS ON COMBINED EFFECT OF WELDING RESIDUAL STRESS AND AXIAL COMPRESSIVE LOAD ON BUCKLING CAPACITY OF THIN LOW CARBON STEEL PLATES

Arc welding is the most commonly used metal joining process and its broad range of applications from large structural fabrications such as bridges to delicate satellite and aerospace components. Welding Residual Stress (WRS) and cracks developed during welding, reduce the quality of welds. Aerospace structures are normally fabricated using thin metal sheets to reduce mass and are always susceptible to buckling. Many researchers have published WRS numerical models and experimental validations, but the impact of WRS on the buckling of thin low carbon steel plates is yet to be studied. The main objective of this study is to analyse the influence of external compressive load and tendon force generated by welding residual stress on buckling strength of the TIG welded low-carbon steel plates. Linear buckling of welded plates under the combined effect of external compressive load and WRS generated due to various weld lengths were numerically modelled and its critical buckling loads are computed. The numerical simulation findings show that the critical buckling strength decreases by 80% when the weld length to plate width ratio (w/wl) is equal to unity and it reduces to minimum when the w/wl ratio is 0.5. After w/wl ratio is 0.5, buckling strength increases and this behavior is caused by the stress field interaction that arises from both the applied axial compressive load and the WRS on the plate.

Effect of heat treatment on microstructure and functional properties of additively manufactured NiTi shape memory alloys

Additive manufacturing of NiTi shape memory alloys has attracted attention in recent years, due to design flexibility and feasibility to achieve four-dimensional (4D) function response. To obtain customized 4D functional responses in NiTi structures, tailorable phase transformation temperatures and stress windows as well as one-way or two-way shape memory properties are required. To achieve this goal, various heat treatments, including direct aging, annealing and annealing followed by aging, were optimized for the Ti-rich NiTi (Ni49.6Ti (at. %)) fabricated by laser powder bed fusion (L-PBF). Microstructural evolution, phase transformation, precipitation and shape memory behaviour were systematically investigated by multiscale correlative microstructural, differential scanning calorimetry analysis and thermomechanical analysis. Based on optimized heat treatments, ∼25 K phase transformation temperature windows and ∼90 MPa stress windows were achieved for the one-way shape memory effect. Solutionized annealing was found to be the most effective way to improve one-way shape memory degradation resistance, due to the reduction of defects and solid solution strengthening. One of the main findings of this study is that the heterogonous microstructures between hard intergranular Ti2NiOx and soft NiTi matrix, induced by solutionized annealing with subsequent aging, result in strain partitioning and enclosing the internal stress state, which was found to promote a pronounced two-way shape memory effect response. The results of this work provide in-depth knowledge on tailoring and designing functional shape memory characteristics via heat treatments, which contributes to expanding L-PBF NiTi application fields, such as biomedical implants, aerospace components, and other advanced engineering applications.

Cutting performance of binderless nano-polycrystalline cBN and PcBN milling tools for high-speed milling of hardened steel

Since difficult-to-machine materials are widely used in high-end equipment such as aerospace and marine components as well as precision molds, the development of high-performance cubic boron nitride (cBN) tools has been an important area of research. In this paper, we evaluate a new type of finer-grained, binderless end mill (binderless nano-polycrystalline cBN, BNNC) by comparing it to polycrystalline cBN (PcBN) end mills for high-speed machining of hardened steel. First, the process of tool preparation based on the above novel cBN is described and high-speed milling experiments were designed. Then, the cutting performance of the BNNC and PcBN tools during high-speed milling is analyzed and compared in four aspects: the cutting force coefficients, the friction coefficient of the rake face, the milling temperature and the tool wear. In addition, the wear mechanism of the two types of end mills was analyzed by energy dispersive X-ray (EDX). Afterwards, the trend of cutting temperature was further investigated by 2D finite element simulation. Finally, grey correlation analysis was applied to describe the correlation between the above factors and tool wear. This study shows that compared with PcBN end mills, BNNC end mills have longer tool life under the same cutting condition and are more reliable at high temperatures, which exhibit great application potential.