Threshold Stress for High-Temperature Creep in Particle Strengthened Al-1.5 vol%Be Alloys

Three Regions of Dislocation Creep in <I>In Situ</I> TiB Fiber-Reinforced &alpha;-Titanium Matrix Composite

“…Using the spacing between the reinforcements, the threshold stress is expected to be around 1 MPa, 12) which is much lower than the measured range.…”

“…Thus the threshold stress by the void strengthening mechanism 12) appears. Region I is characterized by threshold stress behavior which is demonstrated by P/M Al MMCs and DSAs.…”

“…Region I is characterized by threshold stress behavior which is demonstrated by P/M Al MMCs and DSAs. [10][11][12][13][14][15][16][17][18] In the region where the applied stress is sufficiently higher than the threshold stress and the strain rate is lower than the diffusional-accommodation rate, the strain mismatch is accommodated completely and the reinforcements support no external load. In this region (region II), the strengthening by reinforcements disappears and weakening occurs since the volume fraction of the load supporting matrix is smaller than unity, then the strain rate of the composites is higher than that of the monolithic matrix.…”

“…The understanding of the contribution of the reinforcements in strengthening the composite materials in creep, in particular under steady-state condition, has been established in the following two ways: the load transfer concept [1][2][3][4][5][6][7][8][9] based on continuum mechanics and the threshold stress concept [10][11][12][13][14][15][16][17][18] based on dislocation theory.…”

“…The interaction has been interpreted by the Orowan mechanism 20) or the void strengthening mechanism, 21) and the latter is, now, believed to operate at high temperatures. 12) In P/M Al-based MMCs, [13][14][15] a large threshold stress is generated by uncontrolled fine oxides introduced through the processes. The effect of the coarse reinforcements on the creep resistance has been only discussed via estimation of the effective stress, defined as the applied stress minus the threshold stress.…”