THE MICROSTRUCTURAL CHARACTERIZATION OF ND-FE-B ALLOYS .1. LIGHT-ELEMENT MICROANALYSIS

Analyses of oxygen and boron with spatial resolutions of a few mum hav e been carried out using wavelength dispersive X-ray spectrometry (WDX ) in a SEM on an as-cast Nd15Fe77B8 alloy (annealed at 1100-degrees-C for 1 h, followed by furnace cooling) and a laboratory produced [hydro gen decrepitation (HD) route] Nd16Fe76B8 sintered magnet. The optimum experimental parameters including standards, accelerating voltage and analysing crystal were determined. Excellent apparent concentration re producibility has been achieved. Area/peak factors (APFs) for boron K for the Nd2Fe14B matrix phase and Nd(1+epsilon)Fe4B4(epsilon approxima tely 0.1) boron-rich phase have been determined with a Pb stearate cry stal on a JEOL 840A SEM relative to a pure boron standard. The integra l intensity ratios were corrected using both the commercial LINK on-li ne ZAF-4 (FRAME-C) programme and the COR-2 programme. Probably the bes t accuracy of boron measurements has been achieved by use of APFs and the COR-2 programme (equipped with Heinrich's mass absorption coeffici ents). In contrast, the boron results (pure boron standard) from the o n-line ZAF-4 programme are much higher than the reported stoichiometri c concentration of the matrix and the boron-rich phase, although this has been improved by the use of an FeB standard. The mass absorption c oefficient for oxygen absorbed by Nd derived from pure Nd2O3 powder us ing the convergent beam technique (for thickness determination) and ul tra-thin window EDX on a TEM is reasonably close to Heinrich's and Hen ke's values. The results show that the triple junction regions and the Nd2Fe14B-Nd2Fe14B grain boundaries contain the Nd-rich phase with Nd: approximately 90 at%, Fe: approximately 1 at%, oxygen: 8-9 at% and bo ron: < 1 at%. Auger spectroscopy results show that the oxygen present in the matrix phase and in the boron-rich phase exists only in the sur face layer. By contrast the oxygen reacted with the Nd-rich boundary p hase to form a bulk oxide.