A systematic analysis of good matching sites between two lattices

The geometrical matching/mismatching of lattices overlapped in 1, 2 and 3 dimensions have been analyzed systematically by variation of lattice misfit in a large range, far beyond the limits for semicoherent interfaces. In order to evaluate the degree of matching, the density of good matching site （GMS） between two lattices is calculated. The analysis shows that the GMS density remains approximately constant, irrespectively to the degree of lattice misfit. This constant, defined as the average GMS density, decreases exponentially with the increasing dimension of misfit. Typically, for 6 = 15%, the average GMS densities are approximately 30%, 7%, and 1.4% for 1D, 2D, and 3D lattice misfits, respectively. The GMS density deviates significantly if a CSL of small X can be defined. The relationship between the GMS distribution and O-lattice is investigated. It indicates that an abrupt increase in the GMS density in an interface parallel to a principal O-lattice plane is equivalent to a reduction of dimension of misfit. This shows the agreement between the selections of principal O-lattice planes as candidates of the preferred interfaces and the condition that interfaces with high GMS density are preferred.

Interpretation of the Habit Plane of d Precipitates in Superalloy Inconel 718

A calculation method based on a combination of Dg parallelism rule, good matching site（GMS） analysis, CSL/DSCL（coincidence site lattice/displacement shift complete lattice） and the O-lattice theory has been applied to interpret the observation of the habit plane（HP） of the d precipitates and the linear defects in the HP in an Inconel 718 superalloy. The small scattering in the HP orientation around an ideal rational plane is interpreted by the existence of a mixture of two types of steps with different heights and inclinations. These steps play a significant role to enhance the degree of matching in the HP. They are associated with secondary dislocations, with Burgers vectors of 1/6 （1 1 2）y/1/3（0 0 1）, and with a direction parallel to a near-invariant line along （110）y. The spacing of the secondary dislocations projected on the terrace plane is around 6.3 nm. The calculated dislocation structure is in good agreement with the observation.

Newly observed irrational crystallographic features of non-basal Mg_(2)Sn precipitates in a Mg-4Sn alloy aged at 160℃

Two novel types of irrational orientation relationships(ORs)betweenβ-Mg_(2)Sn precipitates and theα-Mg matrix were observed in a Mg-4 Sn alloy aged at 160℃.In contrast to that for the dominantβ-Mg_(2)Sn laths lying on the(0001)_αbasal plane of the matrix,the precipitates with the irrational ORs are inclined or normal to(0001)_α.Specifically,the precipitates that adopt the OR of[011]_(β)//[2110]_α,with(111)_(β)deviating approximately 4.7°from(0002)_α,have a long axis parallel to[0001]_α.The precipitates with the OR of[011]_(β)//[2110]_α,with(111)_(β)deviating approximately 13.50 from(0002)_α,exhibit a long axis of[0211]_α.Both types of precipitates have a habit plane(HP)of(2110)_α.The interface orientations of the precipitates associated with the irrational ORs are interpreted by a good matching sites(GMS)method.A thorough examination of the crystallographic features of theβ-Mg_(2)Sn precipitates in the literature shows that the precipitates with most rational ORs have a HP parallel to(0001)_α,and those with most irrational ORs have a HP(or long axis)inclined or normal to(0001)_α.The preferences of the precipitates with different irrational ORs have also been analyzed by examining the lattice matching condition across the interfaces between the precipitates and the matrix.