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The habit planes observed in numerous alloys during phase transformation can often be explained with the condition that the interface contains a single set of dislocations. Based on the unique matching condition in the habit plane, an analytical expression of the interface orientation in a general system has been derived. The orientations of habit planes are found to be confined on an elliptic cone corresponding to a particular Burgers vector. A simple method based on a superimposed diffraction pattern in the zone axis of the Burgers vector is proposed to specify the axes and parameters of the cones. The present analytical method provides a convenient mathematical tool for a systematic investigation of possible habit planes generated from either martensitic or precipitation transformation. The applications of the method to fcc/bct and hcp/bcc systems are presented. The calculated results have been tested against data in the literature, showing full agreement.

Transition matrix, combine with high-resolution transmission electron microscopy (HRTEM) and stereographic projection, was used in this article to predict and characterize the orientations and electron diffraction patterns of β″ precipitates in Al-Mg-Si-(Cu) alloys. It was found that the β″ phases as the main strengthening precipitates had 12 variants with Al matrix, and the orientation relationships could be expressed as (010) β″//{100}Al, [001] β″//〈310〉Al, and [100] β″//〈230〉Al. Further, based on the C-centered monoclinic structure of β″ precipitate, a new diffraction patterns model under the [001]Al zone axis could be established, which was in good agreement with the experiment date. Further, it could be used to explain reasonably some issues (for example, the “cross-shaped” diffraction streaks phenomenon). Simultaneously, we also found that the β″ precipitates had only three different zone axes, [010] β″, [304] β″, and $$ \left[ {\bar{1}06} \right]_{{\beta^{\prime \prime } }} , $$ parallel to the [001]Al direction when they were precipitated from the Al matrix, and the β″ precipitate might deviate 1.6 deg from its original orientation because of the lattice relaxation.

Transmission electron microscopy (TEM) was performed to study the types of dislocations and their configurations in a commercially extruded ZK60 magnesium (Mg) alloy. We mainly employed the weak-beam dark-field (WBDF) technique with $$ \left\langle {01\overline 1 0} \right\rangle $$ zone axis to unambiguously identify Burgers vectors of various types of dislocations in the microstructure. It was found that nonbasal 〈a〉 dislocations and 〈c〉 dislocations were predominant. No 〈c + a〉 was observed. Rearrangement of these dislocations, due to dynamic recovery during extrusion, led to cell walls and low-angle grain boundaries with relatively high density dislocations. Dissociation of the 〈c〉 dislocations with a relatively narrow split distance was observed. The dissociated 〈c〉 dislocations could form a nodular structure. Fringes of stacking faults from the dislocation dissociation were observed.

TheZ-phase Cr(V,Nb)N particles in various 9 to 12 pct Cr creep-resistant steels were investigated with electron diffraction, energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS). In addition to the well-known tetragonal crystal structure forZ phase, a cubic crystal structure was identified for Cr(V,Nb)N and CrVN particles, but not for CrNbN. The tetragonal and cubic crystal structures were observed to coexist within the same particles, and the orientation relationship between the two lattices was determined. Understanding and controlling the nucleation of Cr(V,Nb)N particles could be of crucial importance to enable improvement of the long-term creep stability of 9 to 12 pct Cr martensitic steels.

The compressive behavior at room temperature of Ti-6Al-4V/TiC composites was examined at strain rates from 0.1 to 1000 s−1. As little as 1 vol pct TiC particulates provided greater than a 20 pct increase in strength over that of the monolithic Ti-6Al-4V, while further additions of TiC did not provide proportional benefits. Microstructural examination before and after compression testing was instrumental in understanding the relative importance of the primary strengthening mechanism in the composites as compared to the monolithic material. A comparison of the various possible mechanisms clearly showed that the dominant mechanism was due to carbon in solid solution. At low strain rates, the failure process consisted of a progression of damage in the matrix and at particle-matrix boundaries, while at high strain rates, failure occurred along adiabatic shear bands. The composites had a greater susceptibility to adiabatic shear-band formation than did the monolithic material.

Solidification of Al-Si alloys typically yields regions of a eutectic mixture of aluminum and silicon phases. In 319-type and 356 aluminum alloys, we have determined that a small percentage (10 to 25 pct) of the silicon phase contains small (10 to 15 nm) equiaxed precipitates of aluminum as identified by electron diffraction with an orientation relation to the silicon matrix: $$[001]_{Si} \parallel [111]_{Al} ;[111]_{Si} \parallel [001]_{Al} ;and(110)_{Si} \parallel (1\bar 10)_{Al} $$ . These precipitates are typically distributed in bands in the silicon and their morphology is insensitive to solidification time and subsequent heat treatments. Energy-dispersive X-ray (EDX) analysis showed that, depending on the alloy, these precipitates contained aluminum, copper, and traces of oxygen.

A method has been developed to determine the density of the Mg2Si β″ and β′ phases in 6xxx aluminum alloys using transmission electron microscopy (TEM). Age-hardened extruded profiles of an AlMgSi alloy, having different coarseness in the precipitate structure, were examined. By darkfield (DF) imaging, β″ needles aligned in a 〈100〉 viewing direction were brought into contrast. Thickness was determined within 10 pct using a spot contamination method. After subsequent corrections, the number density of precipitates could then be quantified, usually within 5 pct. As expected, the average number density of the β″ precipitates correlates well with the material’s tensile strength. A density of β ′ was obtained by a similar method. The densities represent maximum values since precipitate-free areas are not considered. Tensile strength is quite sensitive to theratio between the number densities of β′ and β″. By determining the volume of an average β″ or β′ needle, corresponding volume fractions of the phases can be determined. Quantification of these phases could benefit calculations involving mechanical properties of such alloys.

The interface toughness between a laser clad and the substrate determines whether the cladding is useful for engineering application. The objective of this investigation is to correlate the interface properties of laser-clad Ni-AI bronze on Al alloy AA333 with the microstructure and crystal structure of the interface. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDX) are used to examine the interface. In a good clad track, the interface is an irregular curved zone with a varying width (occasionally keyholing structure) from 30 to 150 μm. A compositional transition from the Cu-rich clad (83 wt pct Cu) to the Al-rich substrate (3.2 wt pct Cu) occurs across this interface. Three phases in the interface are identified in TEM: Al solid solution, θ phase, and γ1 phase, as described in the Cu-Al binary phase diagram. In a good clad track, the θ and γ1 phases are distributed in the Al solid solution. In a clad track with cracks, the interface structure spreads to a much larger scale from 300 μm to the whole clad region. Large areas of θ and γ1 phases are observed. The mechanism of cracking at the interface is related to the formation of a twophase region of θ and γ1 phases. To understand the microstructure, a nonequilibrium quasibinary Cu-Al phase diagram is proposed and compared with the equilibrium binary Cu-Al phase diagram. It is found that the occurrence of many phases such as η1η2, ζ1, ζ2, e1, e2, γ0, β0, and β, as described in the equilibrium binary Cu-Al phase diagram, is suppressed by either the cladding process or by the alloying elements. The three identified phases (Al solid solution, θ phase, and γ1, phase) showed significant extension of solubility.

The point group and space group of an unknown Cr-rich phase in Ni alloy laser clads were identified with convergent beam electron diffraction (CBED). Zone axis symmetry analysis showed that the point group of the phase was 6/mmm. Further examination by zero intensity lines (GM lines) revealed the existence of a 63 screw axis and a glide plane. The space group was then identified as P63/mmc. By referring to [0001] zone axis high-resolution electron microscopy (HREM) images, a structure model with 12 Cr atoms at 12k positions and 2 Ni atoms at 2b positions, as listed in space group P63/mmc, was proposed. The alloying elements were considered to be distributed in the Ni lattice. Simulated [0001] and [11–20] HREM images using the proposed model showed a close match with corresponding transmission electron microscopy (TEM) images.