Abstract: Role of liquid phase stability on the glass forming ability (GFA) has been reviewed and the alloy systemshave been analyzed by introducing a contribution factor (wg) to the characteristic temperature Tg, in the gamma parameter. The kinetics of glass formation for various alloy systems has been found to vary with liquid phase stability in metastable state. The GFA of a fragile liquid is found to be more responsive to the contribution of metastable stability compared to strong liquid.
Abstract: The solid-state reactive diffusion between IF-steel and Al was experimentally studied using IF-steel/Al/IF-steel diffusion couples. The specimens were prepared by a roll bonding technique and then annealed at temperatures 773 K for different time span. At the IF-steel/Al interface in the annealed diffusion couple, wavy layer of Al5Fe2 was observed. The average thickness (Tavg) of Al5Fe2 layer monotonically increases with increasing annealing time (t) according to the equation Tavg = k(t)n, where t is time in second. Value of n = 0.5 indicates that interdiffusion through aluminide phase is the rate controlling step. During annealing, IF-steel matrix has undergone recrystallization. Microstructure and hardness measurement of IF-steel shows that recrystallization process completes within 30 min. Effective heat of formation theory has been applied to predict phase formation sequence during annealing of IF-steel/Al/IF-steel diffusion couples.
Abstract: In the present investigation, discontinuous SiC particle reinforced 2014 Al alloy based metal matrix composites have been produced by spray forming process. The composites contained average particle sizes of 17, 30 and 58 μm in the range of 5–11 vol.%. The composites were tested for their compressive flow behaviour, in unlubricated condition, at strain rates of 0.01, 0.1 and 1.0 s−1 and at temperatures of 150, 300 and 450 °C. The flow stress for 30 μm size particle reinforced composite increased with increasing particle content from 0 to 8.5 vol.%, but decreased at 11 vol.%. The flow stress invariably decreased at larger strain values during deformation. The increase in particle size from 17 to 30 μm led to increase in flow stress at 300 °C, whereas, it decreased at 450 °C. The strain rate sensitivity (m) for 30 μm size particle reinforced composite was close to 0.16 up to 8.5 vol.%, whereas, for the composite with 17 μm size particles it decreased to 0.13 with increasing volume fraction up to 8.6 vol.%. The m values increased from 0.13 to 0.15 with increase in particle size from 17 to 58 μm. The variation in flow behaviour has been attributed mainly to particle fracture and debonding at particle/matrix interface, confirmed by microstructural features of the deformed samples. The major particle fracture events were recorded at low temperature and low strain rate of deformation. The composite with 30 μm size particles showed enhanced restoration process based on the low value of calculated apparent activation energy for diffusion (80–100 kJ mol−1). This deformation behaviour of the composites has been discussed in light of microstructural observations and the void formation during deformation.
Abstract: The present study shows feasibility of synthesising steel-aluminium based metal intermetallic laminate (MIL) composites by an industrially viable and repetitive roll bonding process and subsequent annealing. Roll bonding process has been utilised to achieve solid state bonding of interstitial free (IF) steel and aluminium with simultaneous reduction in sheet thickness. Further annealing of roll bonded laminate sheets gives rise to IF steel-aluminides/aluminium multilayer composites. Formation of Al5Fe2 phase at the interface is confirmed by X-ray diffraction (XRD) analysis.
Abstract: The strain-hardening behavior of Al–1 wt.% Sc alloy was studied and compared with that of Al. Al showed a linear hardening, whereas the Al–1 wt.% Sc alloy showed two-stage behavior for the same equivalent true strain up to 2.0. Transmission electron microscopy studies revealed that dislocation pile-up and dynamic recovery control the hardening behavior in Al, whereas the effective pinning by fine Al3Sc precipitates and dynamic recrystallization at large strain are responsible for the two-stage behavior in Al–1 wt.% Sc alloy.
Abstract: The effect of Al3Sc on the flow stress behavior of aluminum–scandium alloy was experimentally verified. The experimental specimens were prepared by quenching to obtain solid solution and then aged to produce Al3Sc phase. One commercial pure aluminum specimen was included for comparison purpose. A specially designed wedge shape was rolled to obtain mechanical deformation up to 75%. Deformation mechanism was studied by the hardness technique. Upon deformation pure aluminum had shown work hardening whereas the aluminum–scandium alloy showed two distinct modes of deformation. At deformations up to 5%, dislocation motion extended across precipitates, hence strain hardening was revealed by flow stress. High deformations mode i.e. beyond 10% was completely controlled by precipitates; this is reflected by the constant value of flow stress.
Abstract: The present investigation is an attempt to develop metal-intermetallic laminate composites based on Ni-Al system. In this study, Ni and Al foils (460 and 90 ÃŽÅ’m respectively) have been used for the development of Ni-Al laminate using accumulative roll bonding technique at 773 K. The laminate composites were then subjected to controlled annealing at 773 K, 823 K and 873 K for 1, 2 and 4 h to affect reaction at the Ni/Al interface leading to intermetallic compound formation. The accumulative roll bonded laminates showed good bonding of layers. Annealing treatment at 773 K led to slow formation of reaction product but maintained the interface integrity. Annealing at 873 K led to de-lamination of individual layers prior to the completion of reaction. A qualitative compositional analysis at the interfaces reflected the formation of Al-Ni copmpounds, and also a gradual compositional gradient across the interface. This process seems to be of promise so far as the continuous production of large scale metal-intermetallic laminate composites are concerned. A further study is underway to circumvent the delamination problems and property evaluation.
