Intermetallic Composites Research Articles

ИССЛЕДОВАНИЕ СВОЙСТВ И СТРУКТУРЫ АЛЮМОМАТРИЧНЫХ КОМПОЗИТОВ, АРМИРОВАННЫХ ЧАСТИЦАМИ TiO2

Alumina-matrix composite materials based on the AA2024 alloy and TiO2 nanoparticles varying from 0 to 7.5 wt. % have been obtained. A study of hardness and wear was carried out and it was found that increasing the content of titanium oxide nanoparticles from 0 to 5 wt.% leads to an increase in hardness from 39 to 64 HRB, with a further decrease to 38 HRB while the wear rate decreases in reverse order. The structure of the material and the wear surface were studied by optical and scanning electron microscopy. It is shown that the wear surfaces have an uneven structure, which indicates that the wear rate is the result of various failure mechanisms. It has been established that the structure of the alloy consists of numerous interdendritic matrix composites and fine precipitates scattered throughout the volume. It is shown that the interdendritic zone is bordered by Al7Cu2Fe and Al(Cu, Mn, Fe, Si). Intermetallic composites Al3TiCu and Al9TiFe have been revealed

A brief review of processing techniques for NiAl intermetallic composites

In recent decades, NiAl intermetallic compounds have become a potential candidate for elevated temperature structural materials for aerospace applications due to their exceptional properties. In-spite of having lucrative properties, one thing that restricts their application are low ductility and fracture toughness at room temperature. Several attempts have been made by the researchers to overcome these bottlenecks by adopting feasible processing routes. In this paper, an attempt has been made to highlight the various processing techniques with a view to indicate the most suitable technique for the development of NiAl intermetallic composites.

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs).

In as-cast (AC) or heat-treated (HT) metallic ultra-high temperature materials often "conventional" and complex-concentrated (CC) or high-entropy (HE) solid solutions (sss) are observed. Refractory metal containing bcc sss also are contaminated with oxygen. This paper studied the stability of CC/HE Nbss and the contamination with oxygen of Nbss in RM(INb)ICs, RM(Nb)ICs/RCCAs and RM(Nb)ICs/RHEAs. "Conventional" and CC/HE Nbss were compared. "Conventional" Nbss can be Ti-rich only in AC alloys. Ti-rich Nbss is not observed in HT alloys. In B containing alloys the Ti-rich Nbss is usually CC/HE. The CC/HE Nbss is stable in HT alloys with simultaneous addition of Mo, W with Hf, Ge+Sn. The implications for alloy design of correlations between the parameter δ of "conventional" and CC/HE Nbss with the B or the Ge+Sn concentration in the Nbss and of relationships of other solutes with the B or Ge+Sn content are discussed. The CC/HE Nbss has low Δχ, VEC and Ω and high ΔSmix, |ΔHmix| and δ parameters, and is formed in alloys that have high entropy of mixing. These parameters are compared with those of single-phase bcc ss HEAs and differences in ΔHmix, δ, Δχ and Ω, and similarities in ΔSmix and VEC are discussed. Relationships between the parameters of alloy and "conventional" Nbss also apply for CC/HE Nbss. The parameters δss and Ωss, and VECss and VECalloy can differentiate between types of alloying additions and their concentrations and are key regarding the formation or not of CC/HE Nbss. After isothermal oxidation at a pest temperature (800 oC/100 h) the contaminated with oxygen Nbss in the diffusion zone is CC/HE Nbss, whereas the Nbss in the bulk can be "conventional" Nbss or CC/HE Nbss. The parameters of "uncontaminated" and contaminated with oxygen sss are linked with linear relationships. There are correlations between the oxygen concentration in contaminated sss in the diffusion zone and the bulk of alloys with the parameters ΔχNbss, δNbss and VECNbss, the values of which increase with increasing oxygen concentration in the ss. The effects of contamination with oxygen of the near surface areas of a HT RM(Nb)IC with Al, Cr, Hf, Si, Sn, Ti and V additions and a high vol.% Nbss on the hardness and Young's modulus of the Nbss, and contributions to the hardness of the Nbss in B free or B containing alloys are discussed. The hardness and Young's modulus of the bcc ss increased linearly with its oxygen concentration and the change in hardness and Young's modulus due to contamination increased linearly with [O]2/3.

Powder-metallurgy fabrication of ZrB2–hardened Zr3Al2 intermetallic composites by high-energy ball-milling and reactive spark-plasma sintering

A powder metallurgy route combining high-energy ball-milling (HEBM) of elemental powders and reactive spark-plasma sintering (SPS) is proposed for the controlled fabrication of novel composites based on a Zr–Al intermetallic matrix hardened with a ceramic second-phase. As proof-of-concept, its suitability is demonstrated on ZrB2–hardened Zr3Al2. Specifically, commercially available powders of ZrH2, Al, and B were first combined in molar ratios of 2:1:1 to give an intermetallic–ceramic composite nominally formed by ∼76.8 vol.% Zr3Al2 plus 23.2 vol.% ZrB2, and were intimately mixed and mechanically activated by HEBM in the form of dry shaker milling for 30 min, next identifying by a dilatometric SPS test at 50 MPa pressure that the densification window of these composites is ∼975–1275 °C. Subsequent densification SPS tests at 50 MPa pressure in that temperature interval, and also at 1350 °C, plus the microstructural and mechanical characterisations of the resulting materials, established 1175 °C as the optimal SPS temperature. It was also identified that densification takes place by transient liquid-phase sintering with molten Al, and that it occurs gradually, not abruptly, because most molten Al disappears in a flash by reacting with Zr to form in situ the intermetallic. It is also shown that the combination of HEBM plus reactive SPS yields Zr3Al2+ZrB2 composites with fine-grained microstructures formed essentially by multitudinous ZrB2 nanograins dispersed within a matrix of submicrometre, or nearly submicrometre, Zr3Al2 grains. Importantly, these intermetallic–ceramic composites were found to be very hard (i.e., ∼11.5 GPa), attributable to the hardening provided by the ZrB2 nanograins, and fairly tough (i.e., ∼4.5 MPa·m1/2), and therefore potential candidate materials for a multitude of structural–tribological applications. Finally, implications for future study are discussed.

A Study of the Effects of Hf and Sn on the Microstructure, Hardness and Oxidation of Nb-18Si Silicide-Based Alloys-RM(Nb)ICs with Ti Addition and Comparison with Refractory Complex Concentrated Alloys (RCCAs)

In this paper, we present a systematic study of the as-cast and heat-treated microstructures of three refractory metal intermetallic composites based on Nb (i.e., RM(Nb)ICs), namely the alloys EZ2, EZ5, and EZ6, and one RM(Nb)IC/RCCA (refractory complex concentrated alloy), namely the alloy EZ8. We also examine the hardness and phases of these alloys. The nominal compositions (at.%) of the alloys were Nb-24Ti-18Si-5Hf-5Sn (EZ2), Nb-24Ti-18Si-5Al-5Hf-5Sn (EZ5), Nb-24Ti-18Si-5Cr-5Hf-5Sn (EZ6), and Nb-24Ti-18Si-5Al-5Cr-5Hf-5Sn (EZ8). All four alloys had density less than 7.3 g/cm3. The Nbss was stable in EZ2 and EZ6 and the C14-NbCr2 Laves phase in EZ6 and EZ8. In all four alloys, the A15-Nb3X (X = Al,Si,Sn) and the tetragonal and hexagonal Nb5Si3 were stable. Eutectics of Nbss + Nb5Si3 and Nbss + C14-NbCr2 formed in the cast alloys without and with Cr addition, respectively. In all four alloys, Nb3Si was not formed. In the heat-treated alloys EZ5 and EZ8, A15-Nb3X precipitated in the Nb5Si3 grains. The chemical compositions of Nbss + C14-NbCr2 eutectics and some Nb5Si3 silicides and lamellar microstructures corresponded to high-entropy or complex concentrated phases (compositionally complex phases). Microstructures and properties were considered from the perspective of the alloy design methodology NICE. The vol.% Nbss increased with increasing ΔχNbss. The hardness of the alloys respectively increased and decreased with increasing vol.% of A15-Nb3X and Nbss. The hardness of the A15-Nb3X increased with its parameter Δχ, and the hardness of the Nbss increased with its parameters δ and Δχ. The room-temperature-specific strength of the alloys was in the range 271.7 to 416.5 MPa cm3g−1. The effect of the synergy of Hf and Sn, or Hf and B, or Hf and Ge on the macrosegregation of solutes, microstructures, and properties of RM(Nb)ICs/RCCAs from this study and others is compared. Phase transformations involving compositionally complex phases are discussed.

Recrystallization mechanisms during high-temperature XRD and oxidation behavior of CNT-reinforced NiAl composites

In this study, a new perspective is presented on the CNTs-reinforced NiAl intermetallic composites, focusing on the influence of CNT addition on their high-temperature behavior. The obtained results revealed an effective grain boundary pinning effect of CNTs in hindering recrystallization and grain growth of the reinforced composites at high temperatures, leading to significantly smaller grain sizes. CNTs were observed to be beneficial for the high-temperature oxidation resistance at lower concentrations, but detrimental to the oxide scale adherence at higher concentrations. Subsequently, the NiAl-0.5CNT composites exhibited the lowest weight gain due to the stabilizing effect of carbon on the NiAl phase.

Refractory Metal Intermetallic Composites, High-Entropy Alloys, and Complex Concentrated Alloys: A Route to Selecting Substrate Alloys and Bond Coat Alloys for Environmental Coatings.

This paper considers metallic ultrahigh-temperature materials (UHTMs) and the alloying behaviour and properties of alloys and their phases by using maps of the parameters δ (based on atomic size), Δχ (based on electronegativity), and valence electron concentration (VEC), and discusses what connects and what differentiates material groups in the maps. The formation of high-entropy or complex concentrated intermetallics, namely 5-3 silicides, C14 Laves and A15 compounds, and bcc solid solutions and eutectics in metallic UHTMs and their co-existence with “conventional” phases is discussed. The practicality of maps for the design/selection of substrate alloys is deliberated upon. The need for environmental coatings for metallic UHTMs was considered and the design of bond coat alloys is discussed by using relevant maps.

Aging effect on high heat dissipation DBA and DBAC substrates for high power electronics

Direct bonded aluminum (DBA) and direct bonded aluminum with copper (DBAC) substrates were fabricated successfully by transient liquid phase bonding. The 300 nm Ni metallization was deposited on the surface of AlN and joined with Al and Cu to form the DBA and DBAC substrates. After bonding, the discontinuous Al9(Fe,Ni)2 and Al3Ni intermetallic composites (IMCs) were formed at the interface of DBA substrate due to the diffusion of impurities (Fe) in Al and Ni metallization of AlN. As for DBAC substrate, three continuous Al4Cu9, AlCu, and Al2Cu IMCs were formed at the Cu/Al interface. After isothermal aging to 250 °C/2000 h, the bonding area of DBA and DBAC was greater than 98% and the interfacial shear strength of DBA was measured as 40 MPa and the DBAC decreased to 12.5 MPa due to the brittle Al–Cu IMCs at the Al/Cu interface. The unprotected Cu oxide and micrometers size cracks were formed at the surface of Cu in DBAC but no obvious Al oxide and crack in DBA. Even though the thermal conductivity of DBAC is 199 W/mK higher than DBAC substrates (184 W/mK) at room temperature, the thermal stability of DBA is better than DBAC for the applications in high-power electronics.

Core-Shell Particle Reinforcements-A New Trend in the Design and Development of Metal Matrix Composites.

Metal matrix composites (MMCs) are a constantly developing class of materials. Simultaneously achieving a high strength and a high ductility is a challenging task in the design of MMCs. This article aims to highlight a recent trend: the development of MMCs reinforced with particles of core–shell structure. The core–shell particles can be synthesized in situ upon a partial transformation of metal (alloy) particles introduced into a metal matrix. MMCs containing core–shell particles with cores of different compositions (metallic, intermetallic, glassy alloy, high-entropy alloy, metal-ceramic) are currently studied. For metal core–intermetallic shell particle-reinforced composites, the property gain by the core–shell approach is strengthening achieved without a loss in ductility. The propagation of cracks formed in the brittle intermetallic shell is hindered by both the metal matrix and the metal core, which constitutes a key advantage of the metal core–intermetallic shell particles over monolithic particles of intermetallic compounds for reinforcing purposes. The challenges of making a direct comparison between the core–shell particle-reinforced MMCs and MMCs of other microstructures and future research directions are discussed.

Microstructure and fatigue performance of Cu-based M7C3-reinforced composites

Abstract Cu\Fe–Cr–C metal matrix composites (MMCs) were produced with a reinforcer addition of 6, 9, 12, 15, and 18 wt% Fe–Cr–C by powder metallurgy. The effects of sintering temperatures on Cu-based Fe–Cr–C-reinforced composites were studied using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and hardness test. The electrical conductivity and tensile and fatigue strengths of samples were investigated by the conductivity meter and the tensile and fatigue testing machine. The interface microstructure between Fe–Cr–C and Cu particulates at 1000 °C showed a significant difference. The increase in tensile strength, hardness, and fatigue life gave a proportional change with an increase in Fe–Cr–C particulate vol%. The precipitated carbides and intermetallic compositions reduced electrical resistivity depending on the sintering temperature.

Compressive deformation behaviour and toughening mechanisms of spark plasma sintered NiAl-CNT composites

Carbon nanotube (CNT)-reinforced NiAl intermetallic composites were produced via powder metallurgy, particularly spark plasma sintering. The aim of this study was to evaluate the room temperature compressive behaviour of the sintered NiAl-CNT composites with a focus on the toughening mechanisms of the CNT reinforcement and the resulting microstructures. Remarkably, the NiAl-0.5 wt% CNT composites exhibited a balanced combination of strength and toughness despite a trade-off tendency, due to the presence of both coarse and fine bimodal grains in its microstructure. Mechanical properties of 831 MPa, 429 MPa and 360 HV were recorded for the ultimate compressive strength (UCS), compressive yield strength (CYS) and microhardness of the NiAl-0.5%CNT intermetallic composites, respectively, along with a compressive strain of 12% being higher than the unreinforced NiAl.

Thermal reactivity of metastable metal-based fuel Al/Co/AP: Mutual interaction mechanisms of the components

In this paper, a group of novel intermetallic metastable composites Al/Co@AP has been designed, and three methods including ultrasonic dispersion, mechanical grinding and spray-drying have been attempted for their preparation. The latter one has demonstrated to be the most appropriate means, by which the core–shell structured Al/Co@AP with desired properties could be successfully obtained. The thermal reactivity of Al/Co/AP composites prepared differently has been investigated and compared by TG/DSC technique. It has been shown that the heat release rate of AP in DSC curve was largely increased in the presence of Al/Co when spray-drying technique was used, which may be attributed to the increased nuclear site by the intimate contact. The initial reaction temperature of AP in Al/Co@AP was decreased by 7.8 °C and the heat releases by the thermal decomposition of AP and the intermetallic reaction between Al and Co were enhanced by 52.6 % and 67.7% in comparison with that of pure AP and Al/Co. The types of major gaseous products of Al/Co@AP are almost identical to that of pure AP, which include HCl, H2O, N2O and NO2. However, the concentrations of NO2 and N2O in gaseous products for Al/Co@AP are lower than that observed for pure AP, which may be due to the partial consumption of N element by the reaction of Al with acidic substance (HNO3) decomposed from AP. In addition, the AP in Al/Co@AP composite decomposes in one-step with the apparent activation energy (Ea) of 98.8 kJ·cm−3. The decomposition process of the AP in Al/Co@AP composite follows two-dimensional nucleation and growth model(A2), whereas the pure AP follows different physical models, which are close to three-dimensional nucleation and growth, chain scission and phase boundary-controlled reaction (contracting area) models. The intermetallic reaction between Al and Co in Al/Co@AP is merged into one-step following the A2 physical model.

Understanding the Effect of Reflow Profile on the Metallurgical Properties of Tin–Bismuth Solders

Sn–Bi alloys are desirable candidates for soldering components on printed circuit boards (PCBs) because of their low melting point and reduced cost. While certain tin–bismuth solders are well characterized many new alloys in this family have been developed which need proper characterization. The following study looks at the behavior of four different Sn–Bi alloys—traditional 42Sn58Bi and 42Sn57Bi1Ag and two new tin–bismuth alloys—in solder paste during the reflow soldering process. Each alloy was processed using different reflow profiles that had varying times above liquidus (TALs) and peak temperatures. The PCBs were then analyzed to see how the processing variables influenced wetting, voiding, microstructure, intermetallic layer composition, and thickness. After analysis, the PCBs were then subjected to thermal cycling experiments to see how reflow profile impacted microstructure evolution. The results demonstrated that reflow profile affects properties such as metal wetting and voiding. It does not however, greatly impact key metallurgical properties such as intermetallic layer thickness.

On the Microstructure and Properties of Nb-Ti-Cr-Al-B-Si-X (X = Hf, Sn, Ta) Refractory Complex Concentrated Alloys.

We studied the effect of the addition of Hf, Sn, or Ta on the density, macrosegregation, microstructure, hardness and oxidation of three refractory metal intermetallic composites based on Nb (RM(Nb)ICs) that were also complex concentrated alloys (i.e., RM(Nb)ICs/RCCAs), namely, the alloys TT5, TT6, and TT7, which had the nominal compositions (at.%) Nb-24Ti-18Si-5Al-5B-5Cr-6Ta, Nb-24Ti-18Si-4Al-6B-5Cr-4Sn and Nb-24Ti-17Si-5Al-6B-5Cr-5Hf, respectively. The alloys were compared with B containing and B free RM(Nb)ICs. The macrosegregation of B, Ti, and Si was reduced with the addition, respectively of Hf, Sn or Ta, Sn or Ta, and Hf or Sn. All three alloys had densities less than 7 g/cm3. The alloy TT6 had the highest specific strength in the as cast and heat-treated conditions, which was also higher than that of RCCAs and refractory metal high entropy alloys (RHEAs). The bcc solid solution Nbss and the tetragonal T2 and hexagonal D88 silicides were stable in the alloys TT5 and TT7, whereas in TT6 the stable phases were the A15-Nb3Sn and the T2 and D88 silicides. All three alloys did not pest at 800 °C, where only the scale that was formed on TT5 spalled off. At 1200 °C, the scale of TT5 spalled off, but not the scales of TT6 and TT7. Compared with the B free alloys, the synergy of B with Ta was the least effective regarding oxidation at 800 and 1200 °C. Macrosegregation of solutes, the chemical composition of phases, the hardness of the Nbss and the alloys, and the oxidation of the alloys at 800 and 1200 °C were considered from the perspective of the Niobium Intermetallic Composite Elaboration (NICE) alloy design methodology. Relationships between properties and the parameters VEC, δ, and Δχ of alloy or phase and between parameters were discussed. The trends of parameters and the location of alloys and phases in parameter maps were in agreement with NICE.

The Effect of Boron on the Microstructure and Properties of Refractory Metal Intermetallic Composites (RM(Nb)ICs) Based on Nb-24Ti-xSi (x = 16, 17 or 18 at.%) with Additions of Al, Cr or Mo.

This paper is about metallic ultra-high temperature materials, in particular, refractory metal intermetallic composites based on Nb, i.e., RM(Nb)ICs, with the addition of boron, which are compared with refractory metal high entropy alloys (RHEAs) or refractory metal complex concentrated alloys (RCCAs). We studied the effect of B addition on the density, macrosegregation, microstructure, hardness and oxidation of four RM(Nb)IC alloys, namely the alloys TT2, TT3, TT4 and TT8 with nominal compositions (at.%) Nb-24Ti-16Si-5Cr-7B, Nb-24Ti-16Si-5Al-7B, Nb-24Ti-18Si-5Al-5Cr-8B and Nb-24Ti-17Si-3.5Al-5Cr-6B-2Mo, respectively. The alloys made it possible to compare the effect of B addition on density, hardness or oxidation with that of Ge or Sn addition. The alloys were made using arc melting and their microstructures were characterised in the as cast and heat-treated conditions. The B macrosegregation was highest in TT8. The macrosegregation of Si or Ti increased with the addition of B and was lowest in TT8. The alloy TT8 had the lowest density of 6.41 g/cm3 and the highest specific strength at room temperature, which was also higher than that of RCCAs and RHEAs. The Nbss and T2 silicide were stable in the alloys TT2 and TT3, whereas in TT4 and TT8 the stable phases were the Nbss and the T2 and D88 silicides. Compared with the Ge or Sn addition in the same reference alloy, the B and Ge addition was the least and most effective at 800 °C (i.e., in the pest regime), when no other RM was present in the alloy. Like Ge or Sn, the B addition in TT2, TT3 and TT4 did not suppress scale spallation at 1200 °C. Only the alloy TT8 did not pest and its scales did not spall off at 800 and 1200 °C. The macrosegregation of Si and Ti, the chemical composition of Nbss and T2, the microhardness of Nbss and the hardness of alloys, and the oxidation of the alloys at 800 and 1200 °C were also viewed from the perspective of the alloy design methodology NICE and relationships with the alloy or phase parameters VEC, δ and Δχ. The trends of these parameters and the location of alloys and phases in parameter maps were found to be in agreement with NICE.

Development of the technology of microplasma spraying of functional coatings of the nickel – aluminum system for the creation of catalytically active compositions

The results of comprehensive studies on the development of an innovative technology for microplasma spraying of catalytically active systems based on nickel –aluminum intermetallic compositions are presented. A batch of high-capacity chemical current sources based on these compositions with a mass energy level of up to 250 Wt h / kg has been manufactured and tested.

Characterization of Al2O3 Samples and NiAl-Al2O3 Composite Consolidated by Pulse Plasma Sintering.

The paper describes an investigation of Al2O3 samples and NiAl–Al2O3 composites consolidated by pulse plasma sintering (PPS). In the experiment, several methods were used to determine the properties and microstructure of the raw Al2O3 powder, NiAl–Al2O3 powder after mechanical alloying, and samples obtained via the PPS. The microstructural investigation of the alumina and composite properties involves scanning electron microscopy (SEM) analysis and X-ray diffraction (XRD). The relative densities were investigated with helium pycnometer and Archimedes method measurements. Microhardness analysis with fracture toughness (KIC) measures was applied to estimate the mechanical properties of the investigated materials. Using the PPS technique allows the production of bulk Al2O3 samples and intermetallic ceramic composites from the NiAl–Al2O3 system. To produce by PPS method the NiAl–Al2O3 bulk materials initially, the composite powder NiAl–Al2O3 was obtained by mechanical alloying. As initial powders, Ni, Al, and Al2O3 were used. After the PPS process, the final composite materials consist of two phases: Al2O3 located within the NiAl matrix. The intermetallic ceramic composites have relative densities: for composites with 10 wt.% Al2O3 97.9% and samples containing 20 wt.% Al2O3 close to 100%. The hardness of both composites is equal to 5.8 GPa. Moreover, after PPS consolidation, NiAl–Al2O3 composites were characterized by high plasticity. The presented results are promising for the subsequent study of consolidation composite NiAl–Al2O3 powder with various initial contributions of ceramics (Al2O3) and a mixture of intermetallic–ceramic composite powders with the addition of ceramics to fabricate composites with complex microstructures and properties. In composites with complex microstructures that belong to the new class of composites, in particular, the synergistic effect of various mechanisms of improving the fracture toughness will be operated.

Formation of TiAlSi intermetallics during heating Ti-A356 Al mixed powder compact at semisolid temperature

• The local breakage of oxide films determine the formation of τ1 and τ2 crystals and their morphologies. • Both τ1 and τ2 crystals have an intrinsic plate morphology, but τ2 crystals were thinner due to their more anisotropic growth. • τ1 lamellar domains generate during growth of τ2 crystals accompanied by decrease in density of SFs. • τ1 crystals coarsen at the expense of τ2 crystals, leading all reaction products to finally convert into large τ1 plates. Due to the similarity in composition and crystal structure of some TiAlSi ternary intermetallics, it is quite difficult to accurately confirm their physic characteristics, and thus, to tailor microstructure to improve mechanical properties of metal materials related to the TiAlSi intermetallics. Therefore, the formation process of TiAlSi intermetallics was investigated during heating Ti-A356 mixed powder compact at a A356 alloy semisolid temperature of 595 °C. The results indicated that two kinds of intermetallics of τ1 (tetragonal, I41/amd) and τ2 (orthorhombic, Cmcm) generated, and both the concentration and supply direction of Ti atoms, which are related to local breakage of oxide films on neighboring Ti and A356 alloy powders, determined the phase and morphology of the intermetallics. τ1 and τ2 crystals all had an intrinsic plate morphology, but τ2 crystals were thinner due to more anisotropic growth resulted from their high density of stacking faults (SFs). τ1 lamellar domains generated during growth of τ2 crystals, which were accompanied by decrease in density of SFs. The combined effect of size difference and internal energy difference between τ1 and τ2 crystals made large τ1 crystals coarsen at the expense of τ2 crystals in Ostwald ripening, leading them to finally evolve into an agglomerate of large τ1 plates.

Simultaneously improved strength and toughness of hot-rolled brick-and-mortar TiNi/Ti2Ni intermetallic composite

Instead of conventional laminated composite fabricated in industry, the present study successfully, for the first time, produced nacre-like TiNi/Ti2Ni brick-and-mortar composite using industrial hot pressing and hot rolling. In comparison with laminated composite, this brick-and-mortar composite not only exhibited larger compressive strength and flexural strength but also showed higher ductility and initial fracture toughness. These excellent mechanical properties were originated from the brittle Ti2Ni bricks homogenously distributed among the ductile TiNi mortars. Attentionally, this brick-and-mortar microstructure inhibited the delamination between brittle and ductile constituents by stopping the easy crack propagation along the brittle constituent.

On the mechanical properties of Al/Cu-grid/Al intermetallic composite

The present paper deals with the experimental investigation of new process combining static compression with high temperature as a simple way to prepare new Al/Cu-grid/Al metallic composite (MC) that consists of Aluminum matrix and Copper grid acting as ductile reinforcement stacked between the Al sheets. At the stage of composite fabrication, two different thermal cycles were tested to highlight the effect of processing temperature on the layers’ adherence and the mechanical properties of the prepared composites. Consequently, the microstructural and mechanical results revealed that the compression at 630℃ for 30 min, then furnace cooled to 450℃ followed by air cooling led to improved mechanical properties and good adherence of Al sheets.