Alloy Micro Research Articles

Severely weakened extrusion strengthening effect in porthole die extrusion of Al-Mg-Si alloy miniature complex hollow profile under an ultra-large extrusion ratio

Ultra-large extrusion ratio is hardly inevitable during porthole die extrusion of miniature complex hollow profile on industrial horizontal extruders. Although batch extrusion of miniature complex hollow profile has been achieved at ultra-large extrusion ratio, their microstructure and mechanical properties are still unclear. To this end, under the extrusion temperature ranging from 400 ℃ to 480 ℃, a 4×4 mm Al-Mg-Si alloy micro heat pipe profile was extruded at an ultra-large extrusion ratio of 137. The grain size and crystal orientation of the profile were obtained by metallographic and electron backscattered diffraction (EBSD) techniques, and further exploration of the microhardness, tensile properties and pressure-resisting performance were conducted. Interestingly, severely weakened extrusion strengthening effect and low sensitivity of microstructure and mechanical properties to extrusion temperature were observed. Compared to the as-cast extrusion billet, the profile exhibits slight grain refinement and improvement in mechanical performance, and the extrusion temperature does not significantly affect the microstructure and mechanical properties. Instead, as the extrusion temperature increases, the recrystallization fraction generally decreases. These abnormal phenomena are inferred from the fact that even at lower extrusion temperatures, an ultra-large extrusion ratio leads to premature dynamic recrystallization (DRX), and more abnormal growth grains are formed in the profile, weakening the mechanical properties. The higher the extrusion temperature, the earlier DRX occurs, generally forming more abnormal growth and dynamic recovery grains.

Fabrication of Cu-Ni Alloy Microcomponents using Localized Electrochemical Deposition

With the rapid development of electronics, additive manufacturing of complex three-dimensional microscale metal and alloy structures has emerged as one of the future directions for advanced technologies. In this study, a localized electrochemical deposition technique was developed which enables the fabrication of microscale three-dimensional metal structures in an ambient environment. Notably, we investigated the effects of voltage, initial electrode gap, and electrolyte composition on the deposition of Cu-Ni alloy. Furthermore, we successfully fabricated Cu-Ni equiatomic micro-columns, providing possibilities for the micro/nanoscale fabrication of commercial K-Monel copper. Finally, based on these foundations, we successfully shaped overhanging structures with various angles as well as an “H” structure using a rotating cathode substrate, demonstrating their potential in the fabrication of Cu-Ni alloy micro components.

Synergistic phase change and heat conduction of low melting-point alloy microparticle additives in expanded graphite shape-stabilized organic phase change materials

Organic phase change materials (PCMs) have great potential for efficient thermal energy storage and passive thermal management applications due to their non-corrosiveness, high heat storage capacity and stable operating temperature. However, low thermal conductivity and easy leakage seriously restrict the actual application. Meanwhile, heat transfer enhancers typically have a serious negative effect on the heat storage capacity of the PCMs. In this paper, a novel strategy for preparing high performance shape-stable composite phase change materials (CPCMs) is reported, utilizing paraffin wax (PW) as the energy storage material and expanded graphite (EG) as heat transfer enhancers and supporting material, especially in which low melting-point alloy (LMA) micro particles having same phase change temperature as PW are employed with two purposes: one is to provide extra latent heat, and another is to construct a hybrid three-dimensional thermal conduction network in microscale to achieve synergistic thermal conduction with EG. The resulting CPCMs exhibit excellent characteristics in energy storage capacity, thermal conductivity, and thermal cycling stability. The thermal conductivity of ternary CPCM can reach 5.842 W m−1 K−1 when the LMA and EG loading are 4.55 wt% and 9 wt%, which is about 16.4 times higher than that of pure PW, with no obvious volumetric latent heat reduction. This work provides a novel and promising approach for the preparation of CPCMs with high and fast storage properties.

Near zero thermal performance loss of Al-Si microcapsules with fibers network embedded Al2O3/AlN shell

Al-Si alloy, a high temperature phase change material, has great potential in thermal management due to its advantages of high heat storage density and thermal conductivity. Microencapsulation of Al-Si alloy is one of the effective techniques to solve high temperature leakage and corrosion. In this paper, commercial Al-10Si alloy micro powders were encapsulated with flexible ceramic shells whose total thickness is below 1 µm by hydrothermal treatment and heat treatment in N2 atmosphere. The compositions and microstructures were characterized by XRD, SEM and TEM. The shell was composed of AlN fibers network structure embedded with α-Al2O3/AlN which prevented the alloy from leaking and oxidizing, as well as had excellent thermal stability. The latent heat of microcapsules was 351.8 J g–1 for absorption and 372.7 J g–1 for exothermic. The microcapsules showed near zero thermal performance loss with latent heat storage (LHS)/ release (LHR) was 353.2/ 403.7 J g–1 after 3000 cycles. Compared with the published Al-Si alloy microcapsules, both high heat storage density and super thermal cycle stability were achieved, showing promising development prospects in high temperature thermal management.

NiTi SMA Superelastic Micro Cables: Thermomechanical Behavior and Fatigue Life under Dynamic Loadings.

Shape memory alloy (SMA) micro cables have a wide potential for attenuation of vibrations and structural health monitoring due to energy dissipation. This work evaluates the effect of SMA thermomechanical coupling during dynamic cycling and the fatigue life of NiTi SMA micro cables submitted to tensile loadings at frequencies from 0.25 Hz to 10 Hz. The thermomechanical coupling was characterized using a previously developed methodology that identifies the self-heating frequency. When dynamically loaded above this frequency, the micro cable response is dominated by the self-heating, stiffening significantly during cycling. Once above the self-heating frequency, structural and functional fatigues of the micro cable were evaluated as a function of the loading frequency for the failure of each individual wire. All tests were performed on a single wire with equal cross-section area for comparison purposes. We observed that the micro cable’s functional properties regarding energy dissipation capacity decreased throughout the cycles with increasing frequency. Due to the additional friction between the filaments of the micro cable, this dissipation capacity is superior to that of the single wire. Although its fatigue life is shorter, its delayed failure compared to a single wire makes it a more reliable sensor for structural health monitoring.

Micro- and nano-encapsulated metal and alloy-based phase-change materials for thermal energy storage.

An overview of recent literature on the micro- and nano-encapsulation of metallic phase-change materials (PCMs) is presented in this review to facilitate an understanding of the basic knowledge, selection criteria, and classification of commonly used PCMs for thermal energy storage (TES). Metals and alloys with high thermal conductivity can be used as PCMs for rapid heat storage in compact systems owing to their high volumetric TES density. The emerging application of metal PCMs in different fields such as solar thermal energy management, smart wearable devices with thermal comfort control, and cooling of electronic devices call for the need of micro- and nano-TES particles, which can be synthesised in different forms to satisfy specific requirements. As metals are easily oxidised, especially at the micro- and nano-level, encapsulation of metal-based PCM particles is important for sustainable use at high operating temperature in ambient conditions. Recent studies focusing on the encapsulation of metallic PCMs at the micro- and nano-level have been reviewed and classified in terms of the melting point of metal/alloy PCMs used and types of encapsulation materials, such as oxides, polymers, carbon, and metals. The current review is expected to provide an outlook on novel metal and alloy PCMs with function-directed structures and superior TES properties for a broad range of applications.

Design, Fabrication and Vision Based Operational Analysis of Novel Shape Memory Alloy Micro Grippers

Object grip, grasp, hold and place type of tasks incorporate specific engineering design concepts. Considering such principals, eight gripper mechanisms were designed and produced which can be classified as micro grippers due to their small workspace, precise grasping and holding abilities. Common characteristics of all the designs are that, without using any electric motor, the open–close operation is by virtue of shape-memory alloys. Each gripper is designed for different purposes with different operational principles of which four were initially open and the other four were initially closed configurations. Parametric studies were performed by changing the duty cycle and frequency of pulse width modulation using a signal generator followed by measurement of gripper jaw clearance, open–close period, average open–close velocities, gripping force, holding and lifting abilities of the designed gripper mechanisms. Jaw displacement and velocity parameters were computed by image processing of video records captured during the operation of the gripper mechanisms.

Surrogate models for uncertainty analysis of micro-actuator

Intelligent materials such as shape memory alloy have attracted the attention of scientists to innovate applications in micromachining technology. It is worth mentioning that the numerical study of such technology without considering uncertainties in material parameters has shown a great attention. However, material parameters show variability due to the experiment measurement of these parameters. This paper focuses on uncertainty analysis of a shape memory alloy micro actuator with taking into account uncertainties in material parameters. An uncertainty analysis approach combining the finite element method, metamodeling and Monte Carlo simulation is presented in this work. The constructed metamodels are validated and compared by errors measures and cross validation. After that, Monte Carlo simulation is conducted by the approximations provided by the metamodel. The metamodel based probabilistic method used in this paper is considered as an approach with high efficiency for uncertainty analysis in micro actuator.

Performance Improvement of Photovoltaic Module Using an Air-Cooling Micro Finned Heat Sink

In this work, improved PV panel was fabricated by replacing the tedlar layer with aluminum alloy micro pin fin heat sink to increase the heat transfer conduction. Air flow system was designed and implemented to apply force convection on the heat sink, which named MPFHS-PV/T integrated system, to decrease the PV module temperature. The integrated system was tested on 25Jun 2019 in Baghdad climate and the results recorded as flowing: decreasing the PV module temperature by 14.65% along with electrical performance improvement by 13% for the output power and 13.32% for efficiency. The daily averages of electrical efficiency. 1102%, thermal efficiency 40.94% and overall thermal efficiency 51.9%.

Prediction of mesoscale deformation in milling micro thin wall based on cantilever boundary

The micro channel cold plate is very suitable for the application environment of high heat consumption liquid cooling such as PCB plate and multi-layer components. However, at mesoscale, the titanium alloy micro channel cold plate is micro thin-walled structure of cantilever boundary with weak stiffness, which leads to significant deformation and resultant poor machining accuracy during micro milling. To effectively control and reduce micro thin-walled deformation, a 3D FE cantilever model is established to predict dynamic milling deformation of micro thin wall. The constitutive model of titanium alloy (Ti-6Al-4 V) that includes the strain gradient to consider size effect in micro milling, the edge geometry of milling cutter, the thin-walled microstructure, and micro milling parameters is involved in milling modeling of thin wall. Moreover, a series of micro milling experiments for micro thin wall of titanium alloy at different machining parameters were carried out to investigate the law and mechanism of thin wall deformation in milling micro thin wall subjected to dynamic alternating forces. By comparing numerical and experimental deformation of micro thin wall in micro milling, the accuracy and validity of the prediction model based on cantilever boundary are verified, which provides theoretical support and model basis for the deformation control in milling micro channel cold plate at mesoscale.

Research on deformation law and mechanism for milling micro thin wall with mixed boundaries of titanium alloy in mesoscale

At mesoscale, the blade of micro impeller with Ti-6Al-4V titanium alloy (micro thin wall with mixed boundaries) is a thin-walled structure, characterized by small size, low stiffness, high surface precision, complex boundaries, and difficult-to-control machining deformation. To control and reduce the deformation of micro thin wall, it is necessary to study the micro-deformation mechanisms during milling micro thin-wall parts. In side milling of micro thin wall with mixed boundaries, the micro thin wall suffers from dynamic alternating forces, and the deformation modes are complex, so the direct and accurate theoretical modelling is difficult to make. Since the feed speed in milling micro thin wall is less, the small deformation of micro thin wall can be described based on the flexure deformation model of the thin plate subjected to elastic loadings. Firstly, accompanied by the reciprocal theorem of work for a curved thin plate, Kirchhoff-Love small deformation model of micro thin wall is used to establish the deformation equation and boundary conditions of micro thin wall with mixed boundaries under concentrated milling forces. Thus, the obtained boundary conditions are mainly applied to the subsequent finite element simulation of three-dimensional milling deformation of micro thin wall. Then a three-dimensional deformation simulation of the micro thin wall under different milling parameters is carried out by considering the micro-walled structure, material elasto-plastic constitutive model, the stiffness and geometric structure of micro milling tools in finite element method. In the workpiece constitutive modelling, considering the strain gradient plastic model in micro milling of Ti-6Al-4V titanium alloy, the workpiece plastic constitutive model is modified by introducing the intrinsic characteristic length of the material to describe the size effects in mesoscale micro milling. Finally, a series of the corresponding experiments on the milling of titanium alloy micro thin walls are carried out. By comparing and analyzing the experimental values and finite element numerical results of the micro thin-walled deformation, the micro deformation mechanisms in milling of thin wall are revealed. It also verifies the accuracy and effectiveness of this established milling finite element model of thin wall, and provides theoretical basis and technical support for controlling the milling deformation of micro thin-walled parts.

Anomalous Behavior During Nano‐Compression Superelastic Tests on Cu‐Al‐Ni Shape Memory Alloy Micro Pillars

Shape memory alloys are one of the most important families of functional materials due to superelasticity and shape memory properties. In particular Cu‐Al‐Ni alloys exhibit these properties at nanoscale, becoming potentially useful to design new smart MEMS. In this work, an anomalous behavior observed during nano‐compression superelastic tests on Cu‐Al‐Ni shape memory alloy micro pillars is reported. The study is approached by nano‐compression tests on micro and nano pillars milled by focused ion beam. The anomalous behavior on the superelastic effect is manifested by a sudden stabilization of the stress‐induced martensite, which does not undergo the reverse transformation. A transition, from superelastic to pseudoelastic‐twinning behavior, takes place during the nano‐compression tests, and is evaluated through the load‐depth curves and quantified by the mechanical damping coefficient η, which undergoes a sharp change from ultra‐high damping, η > 0.1, down to η ≈ 0.01. The stabilization of the martensite occurs under two different experimental conditions, along cycling and by applying a very high stress during superelastic tests. In both cases, a further recovery of the initial superelastic behavior is registered. The mechanisms responsible for the observed stabilization and recovery are discussed, together with the implications and further requirements for technological applications in MEMS.

Microstructural features and dry - Sliding wear response of MoTaNbZrTi high entropy alloy

In this work, the microstructure, mechanical properties and dry-sliding wear response of MoTaNbZrTi refractory high-entropy alloy were evaluated. The alloy was prepared by vacuum arc melting and its phase formation prediction models were verified in terms of the actual presented microstructural features. Two crystal lattices were identified by X-ray analysis, while a characteristic dendritic morphology was spotted. The alloy's micro and macro hardness took elevated values, while its compression properties were also examined. The alloy's dry-sliding wear response was tested under different experimental conditions (e.g. sliding distances and counter body materials). In all cases, the possible wear mechanisms were suggested with respect to volume loss, wear rate and friction coefficient estimations. The worn surfaces and debris were also examined by SEM/EDS analysis. Finally, a preliminary wear response comparison between the presented system and two other high entropy alloys proved the supremacy of MoTaNbZrTi regarding its tribological behavior.

Built-up edge effects on process outputs of titanium alloy micro milling

Built-up edge (BUE) is generally known to cause surface finish problems in the micro milling process. The loose particles from the BUE may be deposited on the machined surface, causing surface roughness to increase. On the other hand, a stable BUE formation may protect the tool from rapid tool wear, which hinders the productivity of the micro milling process. Despite its common presence in practice, the influence of BUE on the process outputs of micro milling has not been studied in detail. This paper investigates the relationship between BUE formation and process outputs in micro milling of titanium alloy Ti6Al4V using an experimental approach. Micro end mills used in this study are fabricated to have a single straight edge using wire electrical discharge machining. An initial experimental effort was conducted to study the relationship between micro cutting tool geometry, surface roughness, and micro milling process forces and hence conditions to form stable BUE on the tool tip have been identified. The influence of micro milling process conditions on BUE size, and their combined effect on forces, surface roughness, and burr formation is investigated. Long-term micro milling experiment was performed to observe the protective effect of BUE on tool life. The results show that tailored micro cutting tools having stable BUE can be designed to machine titanium alloys with long tool life with acceptable surface quality.

Influence of electrical parameters on morphology of nanostructured TiO2layers developed by electrochemical anodization

Ti6Al4V alloy micro rough surfaces with TiO 2 self-organized nanostructured layers were synthesized using electrochemical anodization in phosphate/fluoride electrolyte, at different end potentials (5V, 10V, 15V, and 20 V). The current – time characteristics were recorded, and the link between current evolution and the morphology of developing oxide layers was investigated. On flat surfaces of Ti6Al4V alloy we developed TiO 2 layers with different morphologies (random pores, nanopores of 25…50 nm, and highly organized nanotubes of 50…100 nm in diameter) depending on electrical parameters of anodization process. In our anodization cell, in optimized conditions, we are able to superimpose nanostructured oxide layers (nanotubular or nanoporous) over micro structured surfaces of titanium based materials used for biomedical implants.

Electrochemical micro machining characteristics of Fe64Ni36 invar film using micro WC rod electrode

The need for products containing micro-features has shown a remarkably and steady growth in many fields of application in recent years. For the development of micro-feature devices, one of the most important technologies is ECMM (ElectroChemical Micro Machining). In numerous non-conventional micro machining, ECMM has merits such as leaving no residual stress and lower surface roughness on machined products and also it is the absence of heat-affected zone around the cutting area. ECMM is one of the most appropriate machining method for Invar alloy micro machining, and little research has focused on the micro groove machining on Invar film. In this paper, the machining characteristics of ECMM for Invar thin film with WC rod electrode is investigated. By controlling applied voltage, machining time and pulse condition, the machined area and depth of groove on Invar film can be controlled. These methods can machine micro groove on thin Invar film, which is very difficult to do by conventional machining method, because the Invar film thickness is only 30 µm. With the increase of applied voltage and machining time, the machined depth and range of machined area became larger. Experimental results show that 60 % duty factor value is suitable for satisfying both machining rate and accuracy. And the surface quality characteristics of the machined area are investigated. For fabrication precise surface Invar film or Invar devices, high frequency condition is essential. The purpose of this study was to confirm possibilities of making grooving pattern on thin Invar film in micro size and cutting invar thin film using ECMM.

マグネシウム合金微細管の開発動向とその応用

マグネシウム合金微細管の開発動向とその応用

Micro resistance weld moulding to fabricate CuSn33 alloy parts

CuSn33 alloy micro parts of different shapes and sizes were successfully fabricated to verify the feasibility of a micro resistance weld moulding (micro-RWM). Cylindrical samples were sintered for 30min at 600°C, 650°C and 700°C and then cooled to room temperature in a furnace. DSC, metallographic analysis, EDS, XRD and micro-hardness testing were used to characterize the performance of the samples. The samples exhibited the same thermal performance before and after sintering but possessed better microhardness prior to sintering. The microhardness and microstructure of the samples were functions of differences in the sintering mechanism and diameter. The size of micro parts suitable for micro-RWM includes a horizontal size of less than 4mm and a height of less than 2mm.

Development of high performance near eutectic Al–Si–Mg alloy profile by micro alloying with Ti

A high performance near eutectic Al–Si–Mg alloy profile is developed by micro alloying with 0.1wt.% Ti. The tensile properties of near eutectic Al–Si–Mg alloy with and without Ti in different processing conditions are tested for comparison. Microstructure evolution is observed by optical, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results show that the yield strength (YS), ultimate tensile strength (UTS) and elongation of 0.1wt.% Ti alloyed A2 alloy reach up to 193 MPa, 296 MPa and 12.3% respectively, the tensile strength of which is about 50% higher than that of as-extruded base alloy and even stronger than that of the base alloy micro alloyed by 0.1wt.% Zr or 0.1wt.% V. Addition of 0.1wt.% Ti has obvious refine effect on the microstructure of as-cast Al–Si–Mg alloy, however, it has minor strengthening effect on the as-cast mechanical properties.

A micro-ultrasonic powder moulding method to fabricate Sn–Bi alloy micro parts

The Sn–Bi eutectic alloy powder in the micro-cavity was melted by ultrasonic vibration and rapidly cooled to form micro parts; no subsequent sintering process was required. Three kinds of Sn–Bi alloy micro gears were successfully fabricated, which verified the feasibility of the micro-ultrasonic powder moulding method. The effect of ultrasonic exposure time on the microstructure and mechanical properties of the micro parts was investigated respectively by metallographic analysis, XRD and tensile testing. Reasonable process parameters for this method were determined, which were sonotrode pressure of 63.5MPa, ultrasonic output power of 2475W and ultrasonic exposure time of 1.5s.