Processing microstructure-property relationship in aluminum-iron-vanadium-silicon alloys produced by atomized melt deposition

A mathematical model was developed for the atomized melt deposition process in which the liquid metal stream is disintegrated into fine droplets by high speed inert gas and the droplets are deposited directly onto the substrate of required geometry. The numerical model determines the droplet velocity, droplet thermal history, cooling rates of droplets, volume fraction solid in the spray of droplets before deposition and thermal history of the deposit. The solidification heat transfer phenomena taking place during atomized melt deposition was analyzed using a finite difference method based on enthalpy formulation. The numerical model was validated by measuring average spray temperature by oil calorimetry and thermal history of the deposit by continuous monitoring of deposit temperatures. Dispersion strengthened Al-8.5%Fe-1.2%V-1.7% Si alloy, used for high temperature applications was used for model validation and processing-microstructure-property correlations. The predicted thermal history of the deposit and average spray temperature were in good agreement with the corresponding measured temperatures. The extent of undercooling and the rate of droplet solidification were correlated with process parameters such as melt superheat, metal/gas flow rates and melt stream diameter. The size distribution and morphology of silicide dispersoids were used to estimate the cooling rate as functions of process parameters. The tensile properties at 25-425{dollar}spcircrm C{dollar}, fatigue crack growth resistance and fracture toughness at {dollar}25spcircrm C{dollar} of these alloys produced with wide variations in dispersoids size and grain size were determined and were correlated with microstructures. The room temperature fatigue crack growth rates and fracture toughness were evaluated for different crack plane orientations of the same alloy produced by planar flow casting and were compared with those of the alloy produced by atomized melt deposition process.; Deformation characteristics of the alloy processed by planar flow casting was studied by examining the stress strain behavior in tension at 25-420{dollar}spcircrm C{dollar} and the stress strain behavior in compression at {dollar}25spcircrm C{dollar} and hardness tests. The as processed planar flow cast alloy showed non linear elastic behavior, flow softening, yield drop, low uniform and total elongation, serrated yielding, stress relaxation, and anomalous strain rate dependence of ductility. The results indicated that greater dynamic recovery due to fine grains ({dollar}<{dollar}0.3 {dollar}murm m){dollar} and an essentially pure aluminum matrix in the as processed planar flow cast alloy contribute to the observed deformation characteristics. Corroborative evidence for recovery processes was obtained by differential scanning calorimetry and hardness measurements of cold rolled and annealed samples.