Lath-like Phase Research Articles

Microstructure evolution and mechanical properties of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite with a crossed-lamellar structure

TiAl alloys with low density, high creep resistance and high temperature performance are considered as candidate materials to replace nickel-based superalloys in the range of 700∼800 °C. However, the intrinsic brittleness of TiAl alloys has always been the biggest bottleneck restricting their development. In this paper, a bioinspired interpenetrating Ti2AlNb/TiAl composite with crossed-lamellar structure was prepared by combining selective laser melting (SLM) and vacuum hot press sintering (HPS) under the condition of 1150 °C/1 h/45 MPa, to improve the strength and toughness of the composite. Meanwhile, the metallurgical defects and microstructure of Ti2AlNb reinforcement skeleton printed under different volume energy densities (VEDs) were investigated, as well as the evolution of the microstructure at the interface region of the composite was systematically studied. What's more, we studied the mechanical properties of the composite including nanoindentation test, room temperature tensile and bending tests. The results show that the VED is 88.89 J/mm3, an almost completely dense reinforcement skeleton (∼99.8 %) is obtained. The interface region can be divided into four different reaction layers, namely LⅠ, LⅡ, LⅢ and LⅣ, due to the diffusion of elements. LⅠ is mainly composed of Othick/thin lath-like phase and O short rod-like phase. LⅡ is mainly composed of B2/β phase, acicular α2 phase and nanoscale ω-Ti3NbAl2 phase. The LⅢ mainly consists of B2/β phase. The LⅣ is composed of α2 phase. The deformability of each phase in the composite: B2/β phase > O phase >γ phase >α2 phase >ω phase. The tensile strength and fracture toughness of bioinspired interpenetrating Ti2AlNb/TiAl matrix composite are increased by 24.0 % and 89.0 %, respectively, compared with TiAl alloy, which is mainly contributed to the strong interfacial bonding between matrix and reinforcement as well as the synergistic effect of Ti2AlNb reinforcement with high strength and toughness.

Lath-like phases formed at an extremely high temperature in a Mg–RE (RE = rare earth)–Al alloy

Lath-like phases formed at an extremely high temperature in a Mg–RE (RE = rare earth)–Al alloy

The mechanism of supplementary cementitious materials enhancing the water resistance of magnesium oxychloride cement (MOC): A comparison between pulverized fuel ash and incinerated sewage sludge ash

Magnesium oxychloride cement (MOC) pastes incorporating supplementary cementitious materials (SCMs) including pulverized fuel ash (PFA) and incinerated sewage sludge ash (ISSA) were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy dispersive X-ray spectrometry (EDX). The result showed that the mechanism of PFA and ISSA in improving the water resistance of MOC paste is similar, even though the molar ratios of the hydration product in the ISSA-incorporated paste and the PFA-incorporated paste were different. The active phases in PFA or ISSA could react with MgO and produce an amorphous phase (amorphous magnesium aluminosilicate gel), which was interspersed with Phase 5 and changed the morphology of Phase 5 to fibroid or lath-like phases. These fibroid or lath-like phases interlocked with each other and also connected with the amorphous phase in the matrix to form a stable compact structure. Therefore, the water resistance of MOC was improved. The ISSA-blended MOC paste had higher water resistance compared to the PFA-blended MOC, which may be due to the different chemical composition of amorphous phase and the dissolved phosphorus from ISSA.

An investigation into the microstructure and mechanical properties of V4AlC3 MAX phase prepared by spark plasma sintering

The present work investigated the effect of spark plasma sintering of V4AlC3 MAX Phase on the microstructure and mechanical properties. Accordingly, Vanadium, Aluminum and carbon-black powders were mixed through a high energy mixer mill for 10 min in an ethanol medium. The direct inserted mixture of Al-V-C systems in a graphite mold was spark plasma sintered at 1350 °C with the initial and final applied pressure of 10 and 30 MPa at the vacuum condition of 20 Pa. The XRD investigations demonstrated the V4AlC3 crystalline phase along VC and Al2O3 as the side-effect reaction products. The microstructure analyses further indicated a perfect lath-like MAX phase with an almost proper growth. The FESEM micrographs of the prepared sample also indicated the formation of the V4AlC3 MAX phase with the lath-like shape. The fracture surface of the specimen also displayed deformed and separate lath-like phases as a result of the bending test. The different loads used for the hardness test demonstrated a deformation zone around the mark indentation. By increasing the applied load in the hardness test, the deformed area was enhanced. The prepared FESEM images from the deformed area showed different crack propagation mechanisms such as separation and branching, deflection, bridging, particles pulling out and breaking. 389 ± 19 MPa of bending strength and 6.74 ± 0.12 GPa of Vickers hardness were obtained for the prepared sample along the almost full densification as 99% of theoretical density.

Effects of strain states on stability of retained austenite in medium Mn steels

Based on uniaxial tensile and plane strain deformation tests, the effects of strain states on the stability of RA (retained austenite) in medium Mn steels, which were subjected to IA (intercritical annealing) and Q&P (quenching and partitioning) processing, were investigated. The volume fractions of RA before and after deformation were measured at different equivalent strains. The transformation behaviors of RA were also investigated. The stability of RA differed across two different transformation stages at the plane strain state: the stability was much lower in the first stage than in the second stage. For the uniaxial tension strain state, the stability of RA corresponded only to a single transformation stage. The main reason was that there were two types of transformations from RA in the medium Mn steel for the plane strain state. One type was that the martensite originated in the strain-induced stacking faults (SISF). The other type was the strain-induced directly twin martensite at a certain equivalent strain. However, for the uniaxial tension state, only the strain-induced twin martensite was observed. Dislocation lines and dislocation tangles were also observed in specimens deformed at different strain states. In addition, complex microstructures of stacking faults and lath-like phases were observed within a grain at the plane strain state.

Cross-sectional analysis of the surface ceramic layer developed on Ti metal by NaOH-heat treatment and soaking in SBF

The surface structure developed on Ti metal after an NaOH and heat treatment and subsequent soaking in a simulated body fluid (SBF) was investigated using cross-sectional analysis involving SEM observations and EDX analysis, as well as an outer surface analysis involving SEM observations, thin-film X-ray diffraction, and Raman spectroscopy. A 1 μm-thick layer, which consisted of lathlike sodium hydrogen titanate (NaxH2-xTi3O7) elongated perpendicular to the surface, formed on the surface of the Ti metal after the initial NaOH treatment. This layer gradually changed into Ti metal at the boundary. The surface layer was densified by the subsequent heat treatment, accompanied by a transformation of the sodium hydrogen titanate into sodium titanate (Na2Ti6O13), rutile, and anatase. The scratch resistance of the surface layer significantly increased after the heat treatment. When this Ti metal with a modified surface was soaked in SBF, apatite began to precipitate in the interior of the surface layer, filled the interspaces of the lathlike phases to integrate with the latter giving a dense composite structure, and grew over the surface layer.

Morphological Study of Apatite Formation on NaOH- and Heat-Treated Titanium Metal

Surface structural change of titanium metal with NaOH and heat treatments and the subsequent soaking in a simulated body fluid (SBF) was investigated by observing cross section of its surface layer by scanning electron microscope. A layer of lathlike phase of sodium hydrogen titanate was formed on the surface of the titanium metal 1 µm in thickness by the NaOH treatment. This was transformed into a layer of lathlike form a little densified of sodium titanate and rutile by the subsequent heat treatment. In SBF, apatite started to precipitate in the interior of the surface lathlike layer, filled the interspaces of the lathlike phases and grew over the surface. This integration of the apatite with the surface lathlike layer might be responsible for the strong bonding of the titanium metal to the living bone.

The rhombohedral phase produced in partially-stabilized zirconia

It has recently been reported that the rhombohedral phase (r-phase) is produced on the abraded surface of partially-stabilized zirconia (PSZ) [1]. The r-phase found in yttria-stabilized PSZ (Y-PSZ) has a different lattice parameter and composition with the ordered phase Zr3Y4012, which is an equilibrium phase in the ZrO2-Y203 system [2, 3]. The r-phase is considered to be a metastable phase which is induced by mechanical polishing, although the stability of the phase has not been clarified yet. This paper aims to report that the r-phase is formed not only on abraded surfaces but also in bulk Y-PSZ of a particular composition. Five ZrO2--Y203 alloys with Y203 content 2.0, 3.1, 4.0, 5.0 and 6.2mo1% were prepared from zirconia and yttria powders with 99.9% purity produced by Rare Metallic Co. Ltd. The oxide powders were mixed in a ball mill followed by pelleting in a steel die. The pellets were sintered at 1400 ° C for 1 h, and then arc-melted. The average weight of arc-melted samples was about 1.5 g. As reported previously [4], the arc-melted samples were black due to oxygen deficiency, but annealing at 1400 ° C for a few hours restored the usual colour. The oxygen deficiency was estimated to be about 1 at% from the increase in weight of a pure zirconia sample by the annealing. EPMA analysis has shown that the samples have a uniform concentration of Y203 on the cross-sectional plane within an accuracy of less than 0.5mo1%. The structures of the alloys were examined by X-ray diffraction, optical and electron microscopy. X-ray diffraction studies have revealed that the arc-melted alloys with 5.0 and 6.2mo1% Y2Oz were composed of cubic and tetragonal phases. Fig. 1 shows an electron micrograph of ZrO25.0molY203 alloy in which the two-phase structure is seen. It was found that the diffraction pattern from the matrix in the two-phase structure was indexed by an fc c lattice with a fluorite structure. However, the forbidden reflections in the fc c lattice often appeared from the lath-like phase in Fig. 1 [5]. From X-ray and electron diffraction data, the lath-like phase was recognized to be a tetragonal phase (t-phase) embedded in the cubic matrix (c-phase). On the other hand, the structure of ZrO2-2 .0mol%Y203 alloy was composed of monoclinic and tetragonal phases. It was found that a phase with a characteristic structure was developed in ZRO2-3.1 and 4.0 mol%Y203 alloys together with cand t-phases. Fig. 2 is an electron micrograph of the phase with a "herring-bone" appearance, which has a different microstructure to the c-phase or t-phase. The structure in Fig. 2 resembles the rhombohedral /3-phase in ZrO2-Sc203 alloys [6, 7], which is believed to be an equilibrium phase [7, 8]. An examination of the diffraction pattern in Fig. 2 has revealed that the pattern is slightly distorted from that of the f c c lattice with a zone axis close to [100] . The angle between 0 2 0 and 0 0 2 reflections is about 91 °, and the reciprocal vector 0 22 is slightly larger than 02 2. Such a distortion is expected from the rhombohedral distortion in the (111) direction of the fluorite lattice. The