The NDDR-behaviour of a series of as-cast alloys given by the general formula Nd16Fe76.xB8Zrx (01~52.0) has been characterised by hydrogen DTA and resistivity studies. It was found that increasing values of x increased the temperature of disproportionation. Microstructural studies of the Nd16Fe75.5Zr0.5B~ alloy showed that a Zr-Fe containing phase present at the grain boundaries in the cast and disproportionated material is transformed during recombination into a Nd-Zr-Fe containing phase. This work shows that it is possible to produce highly anisotropic HDDR material from a non-homogenised Nd16Fe75.5Zr0.5B~ cast alloy without any further additions such as Co or Ga. Under the conditions employed in these experiments it was found that the best properties were obtained for the Wd16Fe75.5B8Zr0,5 alloy with a Br value in the easy direction aif 1.03T and an i N c of 775 kA/m. The high degree of anisotropy was confirmed by optical microscopy (polarised light).

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Details of the important parameters for hot pressing isotropic Nd16Fe76BS HDDR powders are presented. Optimum magnetic properties may he achieved over broad ranges of green compaction pressure .and hot pressing temperature, time and pressure. Isotropic HDDR powders with lower Ndcontents (i.e. Nd14Fe79B7 and N d 1 3 F e 8 0 . 5 B 6 . 5 ) may also be hot pressed to full density to p5oduce magnets with energy products -1 0 0 k J / m and some advantages of hot pressing the lower Ndcontent compositions are stated. The cause of t h e enhanced values of remanence obtained for nominally isotropic hot pressed HDDR magnets i s probably due to some alignment induced during h o t pressing.The ease of hot pressing HDDR powder suggests this process is commercially v i a h l e , particularly as the HDDR powder production p r o c e s s has been estimated to he cheaper than that of t h e MQ powder.

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