LA H. Al-Dawery, E.G. Butler /Composites: Part A 32(2001)1007-1012 pressureless-sintering, as can be seen in Fig 3. This beha- viour supports the claim of the existence of a zirconia inter ace that separates the fibres from the matrix material, leading to high level of fibres debonding. Composites processed with the zirconia-alumina system, as mentioned in this paper, have been found to exhibit damage tolerant mechanical properties. This is a very essential phenomenon for the development of composite components for high temperature high performance applications Two important factors affecting properties of the final composite have been identified. These are processing temperature and matrix. The ultimate performance of 1 00Nm 20KV composites processed using Nextel720 fibres will depend on the processing temperature on a combination of both. The temperature effect is the 3. SEM micrograph of a fractured surface of a standard composite. a degradation of fibres strength as the temperature increases high level of fibre pull-out is seen. The matrix effect, on the other hand, is possible chemical reactions between fibres and matrix materials. To investi This is a significant achievement in the sense that gate both parameters, two sets of experimental work were Nextel M720 reinforced composites can designed. Details of these sets and corresponding results are considerable level of tensile strength at such a high shown in table 1. results showed that there is no significant temperature. It is very important to mention that the above effect of matrix materials on the strength of composite findings can only be achieved when using zirconia as the samples processed at 1200.C. Whereas strength of the interphase material On the other hand preliminary studies resin composite made with fibres preheated to 1200.C was considerable damage to the 206 MPa, a room temperature tensile strength of 194 MPa fibres strength after undergoing a heat treatment at 1200C, was recorded for a ceramic composite processed at the same with an average of 30 MPa for the tensile strength [11]. This temperature. These results clearly indicate that: (1)there is degradation in the tensile properties of the fibres was attrib- no negative effect of the matrix materials on the final uted to a possible chemical reaction between the fibres strength of the composite; and (2)only processing tempera- mullite composition and the deposited NdPOa due to the ture have a significant effect on the mechanical strength acidic nature of the precursor solutions [ll]. Thus, based on these results, it was decided that ZrOz sols are the only 4. conclusions and most suitable and stable interphase material for proces composite samples reinforced with Nextel720 fibres With respect to our work on the combined application of The above findings confirm that the combination of both the zirconia interphase and the alumina matrix in a single the main constituent of the matrix has been an excellent step, it was found that although near to full fibre-tow infil tration was achieved (see Fig 2), it was difficult to establish materials choice, since there was no chemical degradation of the final composite strength comparing to that of the re- a visible coating around the bulk of the fibres. This is due to enforcement materials, i.e. Nextel 720 fibres. It is there- the fact that it is possible that the thickness of the deposite fore decided that this combination should be used as a stan- coating is so small, in a nanometer scale, that it cannot be detected by SEM. However, in one way or another the exis- dard composition for the matrix material in processing of tence of a zirconia solution in the alumina matrix seems to high-temperature high performance CMCs. have played a role, since high strengths were only obtained for those samples fabricated with this combination. Indeed, Acknowledgements le test of these composites has resulted in samples fail- in a composite behaviour with a high level of fibre The author would like to acknowledge gratefully financial Mechanical properties of ceramic and resin matrix composites. Effect of matrix and processing temperatures Type of matri Ceramic Ceramic Resin Resin Resin 000° 1200° 200°C. 1000°C, 1200C, conditions Tensile strengt (MPa)"   &  $       -
.()          $            $        $ &       $    /       1          -317         &           '())
*  $  A) ,3       ?''@ "         &          &      -317           ?''@ "         01(                       -
.() & 5    %        /                     &   &   $ <
 (=    &   $      %   & "            %                    9, $            /         $                                       $   $  &         
 A "  $         /        &         $  &    *    / B         $            "  $        $                "         &   $   & "       "          -
.() &                    "        &        "               &    "  $         %                " ' K       &                '())
* 5         &   '())
*  ()H ,3        'E7 ,3           "     ; <'=    $         &      >  <(=       $  &            " $ &    &       /                                   &                 -
.() &                               *,*
  "   %  %    &  ,,, *2) #,, "  3
  +   /' '44% %4456%4%' ')''
 A 9,            $  &      " ' ,                 "   * * K K K K K K *      ')))
* '  '())
* '   $ ())
* '  7))
* '  C))
* '  ')))
* '  '())
* '  "    <,3= (.4 'E7 (A' A)E 'E4 ACE (4E ()H