A TECHNIQUE FOR THE PREPARATION OF POWDERS FOR EXAMINATION BY TRANSMISSION ELECTRON-MICROSCOPY

Several techniques exist for preparing thin foils from powders that have been incorporated in a nickel matrix by electroplating or electroless plating. The yield and quality of foils are, however, generally inadequate for analyses requiring large numbers of thinned powders. A new technique has been developed that utilizes a plating chemistry that results in an electroless nickel (EN) matrix. Because the technique does not require a conductive substrate, it is applicable to non-conductive powders as well as to metal powders. For metal powders to be thinned electrochemically the technique produces a matrix that will thin uniformly along with the metal powders using standard electropolishing techniques. The EN matrix produced is non-magnetic and the uniformity of the electrochemical thinning of foils prepared by this method allows surface features on the powders such as splat caps to be easily observed. Also, because the technique produces a high yield of thin foils, it is useful in transmission electron microscopy studies that require large numbers of powders to be examined. The technique is illustrated along with the results of transmission electron microscopy studies characterizing the microstructure of nickel-base superalloy powders and plasma spray coating powders as a function of powder size. The powders thinned in these studies include René 95, low carbon Astroloy, AF-115, IN-100, Merl-76, as well as NiCoCrAlY, vacuum-plasma-sprayed coating alloy powders. © 1990.