NEUTRON TEXTURE INVESTIGATIONS ON NATURAL MT . ISA CHALCOPYRITE ORE . PART I : PREFERRED ORIENTATION OF ONE AND THE SAME CHALCOPYRITE SAMPLE BEFORE AND AFTER EXPERIMENTAL DEFORMATION

NEUTRON TEXTURE INVESTIGATIONS ON NATURAL MT. ISA CHALCOPYRITE ORE. PART I: PREFERRED ORIENTATION OF ONE AND THE SAME CHALCOPYRITE SAMPLE BEFORE AND AFTER EXPERIMENTAL DEFORMATION E. M. JANSEN, H. -G. BROKMEIER and H. SIEMES tlnstitut fiir Mineralogie und Lagerstiittenlehre, RWTH Aachen, Wiillnerstr. 2, D-52056 Aachen, Germany 21nstitut fiir Metallkunde und Metallphysik, TU Clausthal, Auflenstelle GKSS Forschungszentrum, PosOeach 1160, D-21494 Geesthacht, Germany


INTRODUCTION
The tetragonal structure of chalcopyrite (CuFeS2) is a derivative of the cubic sphalerite structure (ZnS), where the Cu and Fe atoms alternately occupy the Zn positions along the c-direction. Thus, the unit cell is doubled in c-direction, the ratio ao/c being 1.97.
Chalcopyrite deformation experiments at temperatures up to 500C have been performed by Atkinson (1974), Kelly and Clark (1975) and Roscoe (1975), but without accompanying texture analysis. A successful separation of the chalcopyrite double reflections was obtained by neutron diffraction. The measurements were carded out at the FRJ-2 reactor, KFA Jtilich using a position sensitive detector (PSD) and a subsequent peak profile analysis (Jansen et al., 1991. Five samples from Mt. Isa axially shortened at temperatures of 25, 100, 200, 300 and 400C were investigated. The measured (112), (200), (004), (220), (204), (312), (116), (224), (400) and (008) pole figures were usable to evaluate the preferred orientation. The pole figures of the samples shortened at low temperatures showed four, at higher temperatures two main orientation components, but no fiber texture was detectable. The interpretation of this texture requires the knowledge of the texture of the undeformed material, but X-ray measured slices of the undeformed material didn't show a clear preferred orientation. Thus, a new testing series seemed to be necessary to study the bulk texture of the same sample before and after experimental deformation by neutron diffraction. As the FRJ-2 reactor in Jtilich didn't operate during the last years the neutron measurements were performed at the FRG-1 at Geesthacht, GKSS-Research Centre. But, as the instrument wasn't equipped with a PSD at that time, another method to separate the chalcopyrite double reflections has to be used.

STARTING MATERIAL AND DEFORMATION EXPERIMENTS
Cylindrical specimens of 15 mm diameter and 30 mm length were prepared from the Mt. Isa chalcopyrite ore, which had already been used for earlier deformation experiments . The ore consists of 85% chalcopyrite, 3% pyrrhotite, 1% pyrite and 11% quartz and other minerals, the average grain diameter of chalcopyrite being 0.3 mm. Eight samples were axially shortened at a constant confining pressure of 300 MPa (400 MPa for room temperature) and with a constant strain rate of about 3-10 -5 sec-. Two experiments at temperature of 25, 100, and 200C, and one experiment at 300 were performed, one experiment at 400C failed after a few percent strain. Details of the experimental conditions are given in Table 1.

NEUTRON TEXTURE ANALYSIS
The texture measurements were performed at TEX-2, the neutron texture diffractometer  (Brokmeier, 1989). The structural data of chalcopyrite were used to calculate the theoretical 2-Theta positions of the reflections for a wavelength of 0.134 nm (Cu(111) monochromator). Table 2 gives the first and strongest reflections of the spectrum. Only the weak (101) and the strong (112) (101) and (112) pole figures were also used to calculate orientation distribution functions (ODFs) by means of the iterative series expansion method using the positivity condition (Dahms and Bunge, 1989;Dahms, 1992). From the ODFs the (101) and (112) Figure  1 shows that the agreement of the compared pole figures is very good for the undeformed sample CH8320 as well as for the deformed sample CH8410. So the texture analysis procedure for all undeformed and afterwards deformed samples was the following: measuring the (101)

PREFERRED ORIENTATION BEFORE EXPERIMENTAL DEFORMATION
Before using the neutron diffraction technique for texture analysis, slices from bottom and top of the undeformed sample cylinders were measured by X-ray diffraction. Examples of incomplete X-ray measured (112) and (220/204) pole figures in Figure   2 show, that it was not possible to identify a pervading preferred orientation for the Mt. Isa ore handspecimen. However, the neutron texture analysis gives evidence of a distinct preferred orientation of the ore. The neutron measured complete (101), (112) and calculated (004) pole figures of the eight investigated samples are given in Figure  3. Comparing the measured (101) (204) maximum for this sample, and a minimum in the center of (101). The pole figures of this sample at least give an intimation of a fiber texture. The differences in preferred orientation between a deformation temperature of 300C and lower temperatures point to a change in deformation mechanisms.

CONCLUSIONS
For the special problem of the chalcopyrite preferred orientation the superiority of the neutron beam over the X-rays in texture analysis is evident. As the total specimen volume is measured by neutron diffraction, the statistics of the weak tetragonal (101) reflection of chalcopyrite is sufficient for the ODF calculation. And as the same specimen volume can be measured before and after experimental deformation, real differences in preferred orientation induced by the deformation processes are observable.
If the original texture of a material in axial shortening experiments is a random TEXTURE OF CHALCOPYRITE ORE PT.   distribution, the development of an axial symmetric preferred orientation, a fiber texture, will start at once and will be visible after a few percent strain. A resulting fiber texture was not reached for the Mt. Isa chalcopyrite ore under the applied experimental conditions. In this case a detailed knowledge of the original preferred orientation, which is responsible for this effect, is of great importance. New orientation components can only develop from the original ones, and the deformation mechanisms strongly depend on the orientation of the crystallites to the strain direction. The combination of four main orientation components, after low temperature deformation, and of two components, after high temperature deformation, of earlier neutron texture investigations on Mt. Isa chalcopyrite , can now be explained in the same way as the components in this study. Two different new components developed after deformation at high temperatures, and at lower temperatures one stronger new component besides the relics of the three original components are found.
A change in deformation mechanisms, which is reported for single crystals to occur between 200C and 400C (Hennig-Michaeli and Couderc, 1989), is confirmed in the present study to take place between 200C and 300C.
The results of the present study, particularly the knowledge of the original preferred orientation of the Mt. Isa material, lead to the conclusion, that further neutron diffraction texture analyses on the complete extensive series of earlier deformed Mt. Isa chalcopyrite samples  can give more information about chalcopyrite deformation behaviour (Part II of this contribution, Jansen et al., 1995).