The effect of temperature on load partitioning evolution in magnesium metal matrix composite reinforced with Ti particles using in-situ synchrotron radiation diffraction experiments

The load partitioning between the magnesium and titanium phases in an extruded Mg-15%Ti(vol.%) composite from room temperature up to 300 ℃ using synchrotron radiation diffraction during in-situ compression tests. During compression, the magnesium matrix composite deforms mainly by the activation of the extension twinning system up to 200 ℃. The volume fraction of twins increases with the plastic strain but decrease with the compression temperature. Hard titanium particles bear an additional load transferred by the soft magnesium matrix from room temperature up to 300 ℃. This effect is amplified after yield stress during plastic deformation. Additionally, twins within magnesium grains behaves as an additional reinforcement at low temperature(below 200 ℃) inducing an increase in the work hardening of the composite.

High temperature mechanical behaviour of Mg-6Zn-1Y alloy with 1 wt.% calcium addition:Reinforcing effect due to I-(Mg3Zn6Yi)and Mg6Zn3Ca2 phases

The infiuence of small calcium additions on the high-temperature mechanical behaviour in an extruded Mg-6Zn-l Y(wt.%)alloy reinforced by the I-phase has been investigated.Calcium promotes the formation of the intermetallic Mg6Zn3Ca2 phase instead of 1-phase,which results in a noticeable improvement of the yield strength and ultimate tensile strength of the alloy above 100℃.The strength of the alloys was analysed taking into account the contribution due to the grain size,the crystallographic texture and the volume fraction and nature of second phase particles.In situ synchrotron radiation diffraction experiments have been used to evaluate the load partitioning between the magnesium matrix and the second phase particles(1-and MgeZgCa?phases)in both alloys.The load transfer from the magnesium matrix towards the MgeZihCa?phase is markedly more effective than that for the I-phase over the entire temperature range,especially at 200°C,temperature at which the reinforcement effect of the I-phase is null.

In-situ synchrotron high energy X-ray diffraction study on the internal strain evolution of D019-α2 phase during high-temperature compression and subsequent annealing in a TiAl alloy

The residual stress in the D019-α2 phase is known to be significantly higher than that in the L10-γphase in TiAl alloys after deformation due to the poor plasticity and strong mechanical anisotropy of theα2 phase.However,the internal stress accumulation and relaxation in theα2 phase during high-temperature deformation and annealing are scarcely investigated.In this study,for the first time,the internal strain evolution and load partitioning between theα2 andγphases at high temperatures are characterized by in-situ synchrotron high energy X-ray diffraction(HEXRD)technique.The plastic deformation is at least initiated at a stress of roughly 200 MPa in theγphase and 775 MPa in theα2 phase.The intergranular strains in theα2 phase are generated by the onset of dislocation glide in theγphase,and accentuated with the accumulated dislocations and the ensuing twinning activity.After unloading,great intergranular strains are preserved in theα2 phase constrained by the heavily plastically deformedγphase.During subsequent heating from 400 to 1000℃,the internal strains in theα2 phase are almost fully relaxed by substantial dislocation annihilation and rearrangement in theγphase.During annealing at 800℃,the internal strain relaxation is rapid in the initial 10 min,whereas considerably retarded subsequently.The extent of relaxation after holding at 800℃for 1 h is equivalent to that of heating in an effective temperature range of 680-880℃for 10 min.The in-situ lattice strain measurements with various thermal relaxation schemes provide guidance for the stress relief annealing of TiAl components.