1997 TMS Annual Meeting: Monday Abstracts

SYNTHESIS OF LIGHT-WEIGHT METALLIC MATERIALS II: Session II: Metallic Composites II

Session Chairpersons: C.M. Ward-Close, Structural Materials Center, R50 Building, Defense Research Agency, Farnborough, Hampshire, GU14 6TD, United Kingdom; S. S. Cho, Vice President of Rapidly Solidified Materials Research Center, (RASOM), Chungnam National University, Taedok Science Town, Taejon 305-764 Korea

2:00 pm

PRODUCING METHOD AND MECHANICAL PROPERTIES OF TiB2 PARTICLE REINFORCED HIGH MODULUS STEEL: Kouji Tanaka, Tadashi Oshima, Takashi Saito, Toyota Central Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi, 480-11, Japan

In our effort to develop high modulus steel, titanium diboride (TiB2) has proved to be the best reinforcement because of its high Young's modulus and excellent thermodynamic stability in iron-based alloys. In this paper, mechanical properties of the developed steel and the methods applied to practical parts fabrication are discussed. Conventional P/M techniques, including liquid phase sintering to achieve its full density and reaction sintering using low-cost ferroalloy powders, have been successfully utilised. Tensile strength, fatigue strength, and abrasive wear resistance of the developed steel were investigated in order to evaluate its potential application. These mechanical properties revealed a linear improvement with the increase in TiB2 volume fraction. The developed steel also provided hot workability required in die-forging process. Trial forged parts demonstrated a possibility of producing high performance automobile parts.

2:20 pm

A STUDY ON MANUFACTURING METHOD AND ABRASIVE CHARACTERISTICS OF SUBSIEVE SIZE SiCp REINFORCED A1 ALLOY COMPOSITE: S.W. Han, S.W. Kim, Department of Metallurgical Eng, Chonbuk National University, Chonju, 560-756, Korea

This study aims to manufacture A1 alloy composites reinforced by subside size (3 mm, 5mm, 10mm) SiCr with duplex process of squeeze-infiltration (1st process) and squeeze casting (2nd process) developed in this study, to investigate effects of alloying element and heat exposure on the microstructures and heat and wear resistance of A1-Si-X(Cu, Cr, Ni)-SiCr). In the last process, when the melt is infiltrated into SiCr bed. At the same time, melt is flowed to loser part along the gap between mould and SiCr bed. Then, the melt is filtrated into upper-direction conversely. At infiltrating depth of 30-40% into SiCr bed, the vertical lamellar infiltration is appeared heterogeneously due to lack of the melt and increase of viscosity. Although pre-composite fabricated by 1st process has excellent distribution of SiCp on matrix, the SiCp wt% is high as applying industrial articles. Being modelled, the pre-composite and A1 alloy are squeeze casted follow melted, agitated in the caster. Through these processes, SiCp wt% is freely controlled as well as the distribution is increased owing to active plain on SiCp during agitation of the 2nd process. A1-12Si-2Mg-3Cu-SiCp has the least wear loss amount among all the composites manufactured in this study. But, A1-12Si-2Mg-3Ni-SiCp has the lowest relative ratio of wear loss amount (wear loss amount after 350°C, 70hr exposure)-(wear loss amount before 350°C, 70hr exposure)/(wear loss amount before 350°C, 70hr exposure) at high sliding speed. Composites with 15wt%(10mm)SiCp increased the wear amount with the increase of sliding speed because of change abrasive wear to adhesive or melting wear. But composite with 35wt%(10mm SiCp) decreased wear amount with the increase of the sliding speed because abrasive wear with power debris occur in high sliding speed and wear debris with block type occur in low sliding speed.

2:40 pm

A STUDY ON THE DEVELOPMENT OF HIGH STRENGTH AND WEAR RESISTANCE INTERMETALLIC COMPOUNDS/ALUMINIUM ALLOY MATRIX COMPOSITES BY SQUEEZE CASTING METHOD: D.C. Choi, S.H. Park, C.W. Won, National University, Chungmann Nation University

Recently, particle reinforced A1 alloy matrix composites accomplished weight reduction by utilising A1 alloy matrix and improved wear resistance, heat resistance and mechanical properties. This technique is believed to have advantages compared to the conventional manufacturing process, in that the intermetallic compounds enforcers as well as density and shape of the perform are more easily controlled. In this study, perform composition of 25, 40, 50, 60 and 75at%A1 were manufactured. The perform swelled after the reactive sintering process in the case of 25at%A1 composition. On the other hand, the perform shrinkage in the case of 60at%A1 and 75at%A1 composition. Microstructures of the composite samples squeeze casted at the mould temperature of 500°C and the A1 alloy melt of 610°C were investigated using X-ray diffractometer, energy dispersive spectrometer, micro-vickers hardness and etching experiments. In the case of Fe-25at%A1 and 40at%A1 composites, mixture of the compound and the A1 alloy matrix were observed at the top part of the ingot, whereas small amount of A1 alloy matrix were dispersed within the compound islands at the bottom part. Composite structure were observed throughout the whole sample in the case of 50at%A1, which is the structure initially intended to obtain.

3:00 pm

FABRICATION AND MECHANICAL PROPERTIES OF SQUEEZE CAST Mg MATRIX COMPOSITES: Yoon-suck Choi, Kyung-mox Cho, Ik-min Park, Dept of Metal Eng Pusan Nat Univ. Pusan, Korea

In the present study, AZ91 Mg matrix composites were fabricated with a variation of the applied pressure using squeeze infiltration technique. Alumna short fibre (Saffil and Kaowool) and aluminium borate whisker were chosen as reinforcements. Performs of reinforcements from the slurries with different binder compositions were consolidated by vacuum suction method. Microstructural observation was performed to investigate the effects of reinforcements and squeeze casting condition including applied pressure and preheating temperature of performs etc on the solidification microstructure of the Mg matrix composites. Mechanical properties such as bending strength and fracture toughness were measured to evaluate properties of the squeeze cast Mg matrix composites. In-situ SEM fracture test was performed to observe the fracture process of the Mg matrix composites.

3:20 pm

SYNTHESIS OF MoSi-BASED COMPOSITES: S. Walloe, L. Christodoulou, Department of Materials, Imperial College, London SW7 2BP, UK. P. Goodwin, M. Ward-Close, Structural Materials Centre, Defence Research Agency, Farnborough GU14 6TD, UK

A study has been undertaken to investigate process parameters controlling the formation of moist composites using elemental powder-based reaction synthesis techniques. The size and shape of reinforcement have been correlated to the processing conditions and the starting powder characteristics.

4:00 pm

FABRICATION AND MECHANICAL PROPERTIES OF SQUEEZE CAST MG MATRIX COMPOSITES: Y.S. Choi, K.M. Cho, I.-M. Park, Dept of Metal Eng, Pusan Nat Univ. Pusan, South, Korea

In the present study, AZ91 Mg matrix composites were fabricated with a variation of the applied pressure using squeeze infiltration technique. Alumna short fibre (Saffil and Kaowool) and aluminium borate whisker were chosen as reinforcements. Performs of reinforcements from the slurries with different binder compositions were consolidated by vacuum suction method. Microstructural observation was performed to investigate the effects of reinforcements and squeeze casting condition including applied pressure and preheating temperature of performs etc on the solidification microstructure of the Mg matrix composites. Mechanical properties such as bending strength and fracture toughness were measured to evaluate properties of the squeeze cast Mg matrix composites. In-situ SEM fracture test was performed to observe the fracture process of the Mg matrix composites.

THE FOLLOWING PRESENTATION IS WITHDRAWN
4:20 pm

PHASE FORMATION AND PROPERTIES OF MECHANICALLY ALLOYED Mg-BASED MULTICOMPONENT LIGHTWEIGHT ALLOYS: J. Eckert, N. Schlorke, C.A.R.T. Miranda1, and L. Schultz, Institute fur Festkorper-und Werkstofforschung Dresden, Institute fur Metallische Werkstoffe, D-01171 Dresden, Germany; 1Permanent Address: LIJÓ-Barcelos, Portugal

Multicomponent Mg-Y-Cu lightweight alloys were prepared by mechanical alloying of elemental powder mixtures. The progress of alloying, the resulting phases and their thermal stability were characterised by x-ray diffraction, differential scanning calorimetry (DSC) and thermo-mechanical analysis (TMA). Coexistent amorphous and nanoscale crystalline phases are found for a variety of alloys with different composition. The thermal stability data of the materials as obtained by constant-rate heating DSC and TMA measurements and isothermal annealing experiments are discussed with respect to phase separation in the undercooled liquid state and nucleation and growth of nanocrystalline phases. Some characteristic properties of the glassy phase are presented and discussed with respect to the composition dependence of the glass transition and the crystalline temperature. The results are compared with data for melt-quenched samples. Finally, the influence of processing conditions and contamination effects during milling on the phase formation and the thermal stability of the mechanically attrited powders is critically assessed.

4:40 pm

IRON AND ALUMINIUM MICRO/NANOLAMINATES PROCESSED BY HIGH RATE DEPOSITION: C. Loader, D. Dunford, Z. Kulikowski, C.M. Ward-Close, Structural Materials Centre, Defence Research Agency, Farnborough GU14 6TD, UK

A model iron-aluminium system was employed to understand the toughness characteristics observed in multi-layered materials. The process for fabricating laminates by physical vapour deposition using either thermal or electron beam evaporation is described. Laminates are deposited onto a rotating collector and are typically around 2-4mm thick. In this work a range of laminates were fabricated with layer thickness varying from 10nm to 5mm. Microstructural evaluation of the laminates was performed using SEM, XRD, EPMA, and TEM; mechanical property data was generated using tensiles, four-point bend, notched bend, and microhardness. Results show strength and toughness increases are obtained in multi layered materials compared to monolithics primarily due to crack deflection and blunting. The effect of changing layer thickness on the strength and toughness is reported.

5:00 pm

MICROSTRUCTURE PROPERTY STUDIES IN Fe-Al LAMINATE MATERIALS: G. Shao, P. Tsakiropoulos, C. Loader, D. Dunford,* and C.M. Ward-Close,* Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK; *Structural Materials Centre, Defence Research Agency, Farnborough GU14 6TD, UK

Fe/Al laminates of different layer thicknesses were produced by PVD. TEM studies showed that as deposited microstructure depends on the ratio of the nominal thicknesses of the Fe and Al layers and on the actual layer thickness. For dfe:dal=0.4mm the microstructure consisted of nanocrystals of Fe/Al solid solution with A2 or B2 structure and Al2Fe. For dfe:dAl>>44nm or 2.1mm:0.7mm laminated structures were produced. The laminates consisted of layers of Fe(A2-bcc) and of solid solution of Fe in Al with B2 (ordered bcc) structure which was formed by interdiffusion between the Fe and Al layers. Thermodynamic modelling showed that interdiffusion and interface reaction in the as deposited materials are closely related to the overall heat of mixing. The mechanical properties of the laminates will be related to their microstructures.