Ceramic particles reinforced copper matrix composites manufactured by advanced powder metallurgy:preparation, performance, and mechanisms

Copper matrix composites doped with ceramic particles are known to effectively enhance the mechanical properties,thermal expansion behavior and high-temperature stability of copper while maintaining high thermal and electrical conductivity.This greatly expands the applications of copper as a functional material in thermal and conductive components,including electronic packaging materials and heat sinks,brushes,integrated circuit lead frames.So far,endeavors have been focusing on how to choose suitable ceramic components and fully exert strengthening effect of ceramic particles in the copper matrix.This article reviews and analyzes the effects of preparation techniques and the characteristics of ceramic particles,including ceramic particle content,size,morphology and interfacial bonding,on the diathermancy,electrical conductivity and mechanical behavior of copper matrix composites.The corresponding models and influencing mechanisms are also elaborated in depth.This review contributes to a deep understanding of the strengthening mechanisms and microstructural regulation of ceramic particle reinforced copper matrix composites.By more precise design and manipulation of composite microstructure,the comprehensive properties could be further improved to meet the growing demands of copper matrix composites in a wide range of application fields.

Recently deepened insights regarding Mg corrosion and advanced engineering applications of Mg alloys

This review summarizes recent insights into the Mg corrosion mechanism, clarifies many critical controversial points regarding the Mg corrosion behaviour, and updates some efforts made to extend the industrial application of Mg alloys. Based on the new understandings gained so far, future research directions are also suggested in the review. This review has the following logic. The first section "1. Scope"is a consolidation of the new understandings or developments regarding the Mg corrosion mechanism and the new applications for Mg alloys. It also highlights some key points for the review. The second section "2. Widely accepted knowledge" briefly summarizes the general understanding of Mg corrosion gained so far, which acts as the foundation for the following sections. The third section "3. Recently deepened insights" mainly briefs on some new insights into Mg corrosion phenomena based on recent findings. Different interpretations on the corrosion behaviours are comprehensively discussed in the fourth section "4. Controversial points" and the conclusions are drawn in the subsection"4.5 Clarified points". Apart from the fundamental understandings, various efforts in the application of Mg alloys are presented in the fifth section "5. New applications". Following the research tendency as indicated in the review, prioritized research areas are suggested in "6.Future directions". The review is concluded with "7. Concluding remarks" at last.

New insights on the high-corrosion resistance of UHP Mg-Ge alloys tested in a simulated physiological environment

UHP Mg-Ge alloys was recently found to provide excellent corrosion resistance.This paper provides new insights on the mechanism of improved corrosion resistance of UHP Mg-Ge alloys in Hanks’solution.The studied UHP Mg-0.5Ge and UHP Mg-1Ge alloys showed superior corrosion resistance compared to UHP Mg and WE43,with the Mg-1Ge exhibiting the best corrosion performance.The exceptional corrosion resistance of the UHP alloy is attributed to(i)Mg_(2)Ge’s ability to suppress cathodic kinetics,(ii)Ge’s capability to accelerate the formation of a highly passive layer,and the(iii)low amounts of corrosion-accelerating impurities.

Preface to the Special Issue:Additive Manufacturing—Expanding Production Horizon

Additive manufacturing(AM),commonly known as 3D printing,has become a transformative technology that has a profound impact on various industrial sectors.AM encompasses a set of techniques for building objects layer by layer from digital models.Unlike conventional subtractive manufacturing methods that involve removing material from large blocks,AM adds material incrementally,providing unprecedented design flexibility and efficiency.

A comparative study of the role of solute,potent particles and ultrasonic treatment during solidification of pure Mg,Mg-Zn and Mg-Zr alloys

Ultrasonic treatment(UST)applied during the solidification of pure Mg,eutectic(Mg-Zn)and peritectic(Mg-Zr)alloys was investigated in order to explore the grain refinement mechanisms.Temperature dependent grain refinement is observed in pure Mg where decreasing the superheat temperature(at which UST is applied from above the melting temperature,TM)from 100℃to 40℃produces significant refinement with a uniform grain structure.The presence of solute reduces the temperature dependence of the UST refinement and excellent grain refinement is obtained regardless of the superheat temperature(100℃or 40℃)and even with the use of preheated sonotrode in the Mg-6 wt.%Zn alloy.A further improvement in grain refinement is achieved when the alloy contains potent particles that introduce additional nucleation of grains in Mg-0.5 and 1.0 wt.%Zr alloys(producing an average grain size of≤100μm).At 40℃superheat,UST of Mg-Zn alloys produces excellent refinement(average grain size<200μm)with non-dendritic grains,which is normally achieved only with the addition of grain refining master alloy in the as-cast condition.The enhanced refinement observed in the eutectic alloy is explained through the undercooling imposed by a relatively cold sonotrode combined with high frequency vibrations and acoustic streaming.The advantages of using a cold sonotrode,a low superheat and solute are demonstrated for achieving significant refinement during solidification of Mg alloys under UST without or with a lower addition of grain refining master alloys.

Microstructure modification and corrosion resistance enhancement of die-cast Mg-Al-Re alloy by Sr alloying

The effects of Sr additions on the microstructure and corrosion performance of a Mg-Al-RE alloy in 3.5 wt.%Na Cl saturated with Mg(OH)_(2) have been investigated.Microstructure examination reveals that the Sr addition introduces additional intermetallic phases,refines intermetallic networks and dendritic grains,and improves the network continuity.More Al and rare earth elements can be identified in the intermetallics and grain boundaries or inter-dendrite regions under a transmission electron microscope and secondary electron microscope,respectively.On the Sr-containing intermetallic phases and the refined microstructure,the oxide films become more protective,resulting in more corrosion resistant boundary areas and thus dendrite grain grooves.Hence,the presence of large amounts of intermetallics and boundaries can enhance the corrosion performance of the Mg-Al-RE alloy containing Sr.

Surface modification of biomedical Mg-Ca and Mg-Zn-Ca alloys using selective laser melting: Corrosion behaviour, microhardness and biocompatibility

Magnesium alloys such as Mg–Ca and Mg–Zn–Ca are good orthopaedic materials;however their tendency to corrode is high.Herein we utilize selective laser melting(SLM)to modify the surface of these Mg alloys to simultaneously improve the corrosion behaviour and microhardness.The corrosion rate decreased from 2.1±0.2 mm/y to 1.0±0.1 mm/y for the laser-processed Mg–0.6Ca,and from 1.6±0.1 mm/y to 0.7±0.2 mm/y for laser-processed Mg–0.5Zn–0.3Ca.The microhardness increased from 46±1 HV to 56±1 HV for Mg–0.6Ca,and from 47±3 HV to 55±3 HV for Mg–0.5Zn–0.3Ca.In addition,good biocompatibility remained in the laser processed Mg alloys.The improved properties are attributed to laser-induced grain refinement,confined impurity elements,residual stress,and modified surface chemistry.The results demonstrated the potential of SLM as a surface engineering approach for developing advanced biomedical Mg alloys.

Improving flexural strength of Ti_(2)C-Ti cermet by hot compressive deformation:Microstructure evolution and fracture behaviors

In order to improve the microstructure and mechanical properties,the hot compressive deformation with 50%height reduction at 1100℃was conducted on a Ti_(2)C-Ti cermet.The results showed that the lamellar Ti precipitates in Ti_(2)C grains were transformed to bimodal size distribution,which was approximately 290 nm and 5.8μm in diameter,respectively,after the hot deformation.The bimodal Ti precipitates suppressed{011}cleavage surfaces of Ti_(2)C during flexural fracture,which resulted in an 18.5%increment of strength.This phenomenon can be attributed to the bimodal Ti precipitates that decreased the average crack driving force due to their gentle variation in elastic modulus compared with the monolithic lamellar Ti precipitates.The present work can guide further deformation and mechanical property improvement of Ti_(2)C cermets.

Laser Powder Bed Fusion of Beta-Type Titanium Alloys for Biomedical Application:A Review

Additive manufacturing ofβ-type titanium alloy is expected to replace Ti-6Al-4V alloy in the field of orthopedic implantation because of their low elastic modulus,excellent corrosion resistance,and biocompatibility.After briefly introducing the laser powder bed fusion(LPBF)process and physical phenomena,this paper reviews the recent progresses in LPBF-edβ-type Ti alloys.The strategies to strengthening and tougheningβ-type Ti alloys are critically reviewed.This is followed by the processing routes employed to achieve to low modulus for orthopedic applications,especially a new methodology for tailoring crystallographic orientation called multi-track coupled directional solidification.The effect of processing and compositions on performance metrics ofβ-type Ti alloys included corrosion behavior,and biocompatibility is reviewed.In the end,challenges in additive manufacturing ofβ-type Ti alloys in future are highlighted,with the aim to ensue clinical application of LPBF-edβ-type Ti alloys.

铸态亚稳β钛合金高应变速率动态再结晶机理

针对铸态亚稳β型Ti-5553钛合金,基于热模拟试验,研究了合金在高温高应变速率条件下的热变形行为,并发现了一种全新的动态再结晶机制。结合多种材料表征技术,揭示了新动态再结晶机制的微观组织演变机理,并分析了变形参数对再结晶行为的影响。结果表明:亚稳β钛合金在高温高速率条件下的显著动态软化是动态再结晶和流变失稳共同作用的结果,动态再结晶产生新晶粒的形核位置、尺寸和组织占比都对热变形参数有较高的敏感性。本文发现和揭示的新动态再结晶机制是连续和不连续这两种常见机制混合而成的耦合机制,既包含了引发不连续动态再结晶的晶界应变集中效应,又包括了连续动态再结晶的亚晶旋转形核过程。

快速固结粉末冶金亚稳β钛合金的热加工性与组织性能

本研究设计了一种低成本短流程粉末冶金固结与加工技术制备了亚稳β型Ti-5553合金,主要包括快速粉末热压、单道次锻压和简单退火热处理。研究揭示了合金在加工过程中的组织演变机理、力学性能优化机理和组织性能关系。结果表明:经过在1275℃流动氩气气氛环境的快速热压,所得固结态合金相对密度高、宏微观组织均匀,无明显缺陷。经过单道次锻压及快速退火处理后,合金的微观组织和力学性能得以调控和优化,其微观组织和力学性能都对热处理温度的变化有较高的敏感性。当热处理温度为700℃和750℃时,合金展现出良好的强塑性匹配,抗拉强度和伸长率分别为1335 MPa和6.6%、1215 MPa和7.2%,原因是多级析出相的组织结构可同时稳固合金的力学性能强化效果、提高合金的均匀协调变形能力,使合金具有高强度和可接受的塑性。

Evaluation on the interface characteristics,thermal conductivity,and annealing effect of a hot-forged Cu-Ti/diamond composite

A Cu-1.5 wt.%Ti/Diamond(55 vol.%)composite was fabricated by hot forging from powder mixture of copper,titanium and diamond powders at 1050?C.A nano-thick TiC interfacial layer was formed between the diamond particle and copper matrix during forging,and it has an orientation relationship of(111)TiC//(002)Cu&[110]TiC//[110]Cuwith the copper matrix.HRTEM analysis suggests that TiC is semicoherently bond with copper matrix,which helps reduce phonon scattering at the TiC/Cu interface and facilitates the heat transfer,further leading to the hot-forged copper/diamond composite(referred as to Cu-Ti/Dia-0)has a thermal conductivity of 410 W/m K,and this is about 74%of theoretical thermal conductivity of hot-forged copper/composite(552 W/m K).However,the formation of thin amorphous carbon layer in diamond particle(next to the interfacial TiC layer)and deformed structure in the copper matrix have adverse effect on the thermal conductivity of Cu-Ti/Dia-0 composite.800℃-annealing eliminates the discrepancy in TiC interface morphology between the diamond-{100}and-{111}facets of Cu-Ti/Dia-0 composite,but causes TiC particles coarsening and agglomerating for the Cu-Ti/Dia-2 composite and interfacial layer cracking and spallation for the Cu-Ti/Dia-1 composite.In addition,a large amount of graphite was formed by titanium-induced diamond graphitization in the Cu-Ti/Dia-2 composite.All these factors deteriorate the heat transfer behavior for the annealed Cu-Ti/Dia composites.Appropriate heat treatment needs to be continually investigated to improve the thermal conductivity of hot-forged CuTi/Dia composite by eliminating deformed structure in the copper matrix with limit/without impacts on the formed TiC interfacial layer.

Current understanding of the origin of equiaxed grains in pure metals during ultrasonic solidification and a comparison of grain formation processes with low frequency vibration,pulsed magnetic and electric-current pulse techniques

The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(i.e.independent of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electric current pulse techniques.The dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites(ultrasonic field),wall crystals arising from the cold surface of the mould(electric current pulse,magnetic and pulsed magnetic fields).In all these cases fluid flow provides an additional contribution(e.g.reduced temperature gradients,growth rate and remelting of dendrites)to maintaining an equiaxed grain structure.The origin of equiaxed grains under an external field also depends on the casting conditions(volume and shape of casting)and the type of alloy other than the mechanisms specific to a particular technique.The current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals(magnesium and zinc)subjected to Ultra Sonic Treatment(UST).The role of the temperature range of UST application,time duration and an unpreheated sonotrode are examined with respect to the origin,evolution of equiaxed grain structure,morphology and the columnar to equiaxed transition.The origin of grains was analysed from three fundamental aspects that contribute to refinement(i)heterogeneous nucleation(ii)fragmentation of existing dendrites and(iii)grains produced from the colder surfaces(arising from mould walls or vibrating surfaces as wall crystals).A comparison of UST refinement with mechanical,low-frequency vibration,electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces(sonotrode and mould wall)in influencing grain refinement.

Grain refinement of commercial pure Al treated by Pulsed Magneto-Oscillation on the top surface of melt

Commercial pure Al can be refined by Pulsed Magneto-Oscillation(PMO) treatment applied via a plate induction coil above the top surface of the melt. The proportion of the equiaxed zone area increases with decreasing Height to Diameter(H/D) ratios from 3.5 to1.8 and further to 1.0. Meanwhile, it increases and then decreases with increasing peak current for the three kinds of ingots with H/D ratios of 3.5, 1.8 and 1.0, respectively. However, when the H/D ratio decreases to 0.44, the area proportion of equiaxed zone can reach the maximum value with a lower peak current. FEA software simulation indicates that smaller H/D ratio results in larger current density, electromagnetic force and convection on the top surface of the melt, favoring nucleation and subsequent grain formation. Through evaluating Joule heating effect by PMO, it was found that the proper amount of Joule heating benefits grain refinement. Excessive Joule heating can reduce the size of the equiaxed zone and change the growth morphology of the grains.

A yttrium-containing high-temperature titanium alloy additively manufactured by selective electron beam melting

A yttrium-containing high-temperature titanium alloy(Ti-6Al-2.7Sn-4Zr-0.4Mo-0.45Si-0.1Y, mass fraction, %) has been additively manufactured using selective electron beam melting(SEBM). The resulting microstructure and textures were studied using scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD) and electron backscattered diffraction(EBSD) and compared with the conventionally manufactured form. A notable distinct difference of microstructures is that additive manufacturing by SEBM enables homogeneous precipitation of fine Y2O3 dispersoids in the size range of 50-250 nm throughout the as-fabricated alloy, despite the presence of just trace levels of oxygen(7×10-4, mass fraction) and yttrium(10-3, mass fraction) in the alloy. In contrast, the conventionally manufactured alloy shows inhomogeneously distributed coarse Y2O3 precipitates, including cracked or debonded Y2O3 particles.

Review of Mg alloy corrosion rates

A review of the literature confirmed that the intrinsic corrosion rate of high-purity Mg as measured by weight-loss is 0.3mm/y in a concentrated chloride solution.Atmospheric corrosion of Mg alloys has produced corrosion rates of Mg-Al alloys an order of magnitude lower than the intrinsic corrosion rate of Mg in a concentrated chloride solution of 0.3 mm/y.The only successful strategy to produce a Mg alloy with a corrosion rate in a concentrated chloride solution substantially less than the intrinsic corrosion rate as measured by weight loss of Mg of 0.3 mm/y has been to improve the protectiveness of the corrosion product film.

Biodegradable Zn–3Cu and Zn–3Cu–0.2Ti alloys with ultrahigh ductility and antibacterial ability for orthopedic applications

Zinc(Zn) and its alloys have been proposed as biodegradable implant materials due to their unique combination of biodegradability, biocompatibility, and biofunctionality. However, the insufficient mechanical properties of pure Zn greatly limit its clinical application. Here, we report on the microstructure, mechanical properties, friction and wear behavior, corrosion and degradation properties, hemocompatibility, and cytocompatibility of Zn–3 Cu and Zn–3 Cu–0.2 Ti alloys under three different conditions of as-cast(AC),hot-rolling(HR), and hot-rolling plus cold-rolling(HR + CR). The HR + CR Zn–3 Cu–0.2 Ti exhibited the best set of comprehensive properties among all the alloy samples, with yield strength of 211.0 MPa, ultimate strength of 271.1 MPa, and elongation of 72.1 %. Immersion tests of the Zn–3 Cu and Zn–3 Cu–0.2 Ti alloys in Hanks’ solution for 3 months indicated that the AC samples showed the lowest degradation rate,followed by the HR samples, and then the HR + CR samples, while the HR + CR Zn–3 Cu exhibited the highest degradation rate of 23.9 m/a. Friction and wear testing of the Zn–3 Cu and Zn–3 Cu–0.2 Ti alloys in Hanks’ solution indicated that the AC samples showed the highest wear resistance, followed by the HR samples, and then the HR + CR samples, while the AC Zn–3 Cu–0.2 Ti showed the highest wear resistance.The diluted extracts of HR + CR Zn–3 Cu and Zn–3 Cu–0.2 Ti at a concentration of ≤25 % exhibited noncytotoxicity. Furthermore, both the HR + CR Zn–3 Cu and Zn–3 Cu–0.2 Ti exhibited effective antibacterial properties against S. aureus.

Stress corrosion cracking of high-strength AZ31 processed by high-ratio differential speed rolling

Stress corrosion cracking(SCC)in distilled water was studied for AZ31,processed by differential-speed-rolling to different strengths,using Linear Increasing Stress Tests(LISTs).The stress corrosion crack velocity was 5.0±2.5×10^(−9) m s^(−1),independent of applied stress rate and independent of material strength.SCC susceptibility was greater at lower applied stress rates manifest most importantly as a lower threshold stress for stress corrosion crack initiation.SCC susceptibility could be characterised by the ratio of threshold stress to yield stress,which was dependent on processing details and was as low as 0.3.

Processing of metastable beta titanium alloy:Comprehensive study on deformation behaviour and exceptional microstructure variation mechanisms

Thermomechanical processing(TMP)is especially crucial for metastableβtitanium alloys,which has received significant attention in the community for a long time.In this contribution,the processing-responding behaviour including microstructure evolution process,texture variation mechanism,and un-derlying deformation process of powder metallurgy Ti-5553 alloy in a wide processing parameter range was comprehensively investigated.Thermal physical simulation was performed on the alloy at temper-atures ranging from 800℃ to 1100℃,and strain rates between 0.001 s^(−1) and 10 s^(−1),to varied defor-mation degrees of 20%-80%height reduction.It was found that the processing parameters(i.e.temper-ature,strain rate,and deformation degree)are influential on the deformation process and resultant mi-crostructure.Varied microstructural evolution processes forβphase including flow localization,dynamic recovery,dynamic recrystallization,and grain coarsening are activated in different processing domains,while different evolution mechanisms forαphase including dynamic precipitation,phase separation,dy-namic coarsening,and mechanical shearing also play their roles under different processing conditions.In particular,four exceptional evolution mechanisms ofαprecipitation which have not been previously reported in titanium alloys were discovered and clearly demonstrated,more specifically,they are multi-interior twinning,internal compositing,layered coarsening and selective diffusion-actuated separation.After the establishment of comprehensive microstructural evolution mechanism maps,the guidance for precise processing and the knowledge reserve extension for deformation process of metastableβtita-nium alloys can be effectively achieved.

The influence of Ca and Cu additions on the microstructure,mechanical and degradation properties of Zn-Ca-Cu alloys for absorbable wound closure device applications

Novel ternary Zn-Ca-Cu alloys were studied for the development of absorbable wound closure device material due to Ca and Cu’s therapeutic values to wound healing.The influence of Ca and Cu on the microstructure,mechanical and degradation properties of Zn were investigated in the as-cast state to establish the fundamental understanding on the Zn-Ca-Cu alloy system.The microstructure of Zn-0.5Ca-0.5Cu,Zn-1.0Ca-0.5Cu,and Zn0.5Ca-1.0Cu is composed of intermetallic phase CaZn13 distributed within the Zn-Cu solid solution.The presence of CaZn13 phase and Cu as solute within the Zn matrix,on the one hand,exhibited a synergistic effect on the grain refinement of Zn,reducing the grain size of pure Zn by 96%;on the other hand,improved the mechanical properties of the ternary alloys through solid solution strengthening,second phase strengthening,and grain refinement.The degradation properties of Zn-Ca-Cu alloys are primarily influenced by the micro-galvanic corrosion between Zn-Cu matrix and CaZn13 phase,where the 0.5%and 1.0%Ca addition increased the corrosion rate of Zn from 11.5μm/y to 19.8μm/y and 29.6μm/y during 4 weeks immersion test.