Specific heat of superheated Al-10Sr alloy melts

The specific heat of superheated Al 10Sr melts was determined at different heating rates between 1 K/min and 20 K/min using a differential scanning calorimeter(DSC). As a whole, the specific heat increases with increasing temperature. A hump is observed on the specific heat curve at the temperature corresponding to the phase boundary temperature dependent on heating rate. Moreover, the hump shifts to higher temperature in the measured temperature range from about 840 ℃ to 890 ℃ with increasing heating rate. At certain temperature in the higher superheated zone, the specific heat of the melt as a function of temperature shows a sharp rise . The result indicates that disorder zone fraction begins to increase while atom clusters fraction decreases at the breaking temperature. [

Serrated chip characteristics and formation mechanism in high-speed machining of selective laser melted Ti6Al4V alloys

Serrated chips,consisting of extremely uneven plastic deformation,are a prominent feature of high-speed machining of difficultto-machine materials.This paper focuses on the evolution of chip form,chip morphology features(chip free surface,tool-chip contact surface,and chip edge),and chip segment parameters in subsequent high-speed(vc=50 and 150 m min-1)machining of selective laser melted(SLMed)Ti6Al4V alloys,which are significantly different from conventional Ti6Al4V alloy in microstructure,mechanical properties and machinability.The effect of laser beam scanning schemes(0°,67.5°,and 90°),machined surfaces(top and front),and cutting speeds on serrated chip characteristics of SLMed Ti6Al4Valloys was investigated.Based on the Johnson-Cook constitutive model of SLMed Ti6Al4Valloys,an orthogonal cutting model was developed to better understand the effect of physical-mechanical properties on the shear localization,which dominates the formation mechanism of serrated chips in post-machining of SLMed Ti6Al4V alloy.The results showed that the critical cutting speed(CCS)for chip serration of SLMed Ti6Al4V alloy is lower than that for serrated chips of conventional Ti6Al4V alloy,and the serrated profile of SLMed Ti6Al4V chips was more regular and pronounced.Besides,due to anisotropic microstructure and mechanical properties of SLMed Ti6Al4Valloys,the serration degree of chips produced on the top surfaces of SLMed Ti6Al4Valloys is more prominent than that of chips generated on the front surfaces.In addition,because of the poor deformation coordination and high plastic flow stresses of needle-like martensiteα′,the plastic flow and grain distortion in the adiabatic shear band(ASB)of SLMed Ti6Al4V chips are significantly smaller than those in the ASB of conventional Ti6Al4V with equiaxed grains.