D. L. Martin

Microstructure of aged (Co,Cu,Fe)7Sm magnets

The microstructure of (Co,Cu,Fe)7Sm magnets has been characterized at various states of aging by transmission electron microscopy. At peak magnet properties, the magnet consists of cells of 17 : 2 phase about 500 A in diameter, separated by a thin continuous fully coherent 5 : 1 boundary phase. This structure evolved by precipitation of ordered 17 : 2 particles from a disordered 5 : 1 matrix, and coarsens with aging until full coherence is lost and the cellular structure breaks up. The overaged alloy consists of semicoherent 5 : 1 particles in a 17 : 2 matrix, with a single set of interface dislocations accommodating the lattice mismatch. The effect of these various microstructural changes on domain‐wall pinning and coercivity is discussed.

Phase Equilibria in an Ordering Alloy System

The equilibria between phases in platinum alloys containing 42, 48, and 54 atomic percent cobalt were determined at temperatures below 1000°C. This system of alloys exhibits an order‐disorder transition analogous to that for CuAu. A temperature range in which ordered and disordered phases coexist in equilibrium was determined for each alloy. These data were incorporated in the phase diagram. The Co‐Pt system is the first ordering alloy system in which it has been shown that this reaction is a true phase transformation contrary to the prevalent concepts of the phenomena.

Anisotropy parameters and coercivity for sintered Co5Sm permanent magnet alloys

Saturation magnetization, intrinsic coercive force, anisotropy field, and anisotropy constants were determined for a sample of sintered Co5Sm at 4.2, 77, 300, and 500 °K. The ralationship between the temperature dependence of the coercivity and the anisotropy parameters is discussed.

Cobalt‐Mischmetal‐Samarium Permanent Magnet Alloys: Process and Properties

Several authors have reported successful fabrication of high‐energy product (15–20 MGOe) Co5R‐type cobalt‐samarium permanent magnets. In earlier papers we have described preparation of such magnets by a liquid‐phase sintering process sequence which includes powder preparation, magnetic alignment, pressing, sintering, and magnetizing. We have also described preparation of ternary compositions, primarily Co–Sm–Pr, by this process. In an effort to utilize more abundant rare‐earth metals, the cobalt‐mischmetal‐samarium system has been studied. Initial results indicate that a substantial fraction of the samarium may be replaced with mischmetal and still obtain high magnetic properties (BHmax 20 MGOe). Complete documentation of magnetic properties, i.e., saturation, remanence, coercive force, intrinsic coercive force, (BH)max, and temperature coefficients are presented along with a discussion of the fabrication techniques utilized for preparation of the samples.

INITIAL OBSERVATIONS: COBALT--MISCHMETAL--SAMARIUM PERMANENT MAGNET ALLOYS.

Several authors have reported successful fabrication of high‐energy‐product (20 MG Oe) Co5R‐type cobalt‐samarium permanent magnets. In earlier papers we have described preparation of such magnets by a liquid‐phase sintering process sequence which includes powder preparation, magnetic alignment, pressing, sintering, and magnetizing. We have also described preparation of ternary compositions, primarily Co–Sm–Pr, by this process. In an effort to utilize more abundant rare‐earth metals, the cobalt‐mischmetal‐samarium system has been studied. Initial results indicate that a substantial fraction of the samarium may be replaced with mischmetal while retaining high magnetic properties (BHmax=20 MG Oe).

Ordering reaction in cobalt-platinum alloys

The order-disorder phenomenon in alloys near CoPt composition was studied during the progress of the ordering reaction. The changes in hardness, electrical resistance, X-ray diffraction, and microstructure which accompany the transformation at various temperatures were found to be similar to those characteristic of conventional heterogeneous precipitation reactions. The transformation is discussed in terms of four distinct processes which can appear in the reaction.

``Coil Simulation'' Testing of Niobium‐Tin Wire Samples

The coil simulation test in which the current and field are increased simultaneously along predetermined straight current field lines is used to evaluate the superconducting critical current vs field characteristics of Nb-Sn wires in a solenoid. The critical current field characteristics are presented. (C.E.S.)

Hot Working of Alnico 5 Alloys

Alnico permanent magnet alloys have been successfully shaped into rod, wire and strip by hot working at elevated temperature. It has been found that by careful processing, certain Alnico alloys can be fabricated by extrusion, swaging, and rolling. The wrought Alnico after heat treatment was found to have comparable permanent magnet properties and improved mechanical properties compared to cast specimens of the same alloy.