Wear-resistant boride composites with high percentage of reinforcement phase
A highly wear resistant sintered, hot pressed, or otherwise compacted ceramic composite material is described, consisting of two discrete phases of the form AlxMgyB14 where x and y ≦1 or like hard, orthorhombic compounds, and TiB2 or like Group IVB transition metal di-borides, and with an unexpectedly high contentof transition metal di-boride in the range from 40 to 90 percent (28 to 85 volume percent).
Wear performance of in-situ Al–TiB2 composite
The wear resistance, interpreted as the extent of reduction in wear rate, of in-situ Al–TiB2 composite produced by stir casting route was evaluated by dry sliding wear. Wear evaluation was carried out on composites with varying volume fraction of TiB2, peak aged Al–Cu–15 Vf% TiB2 and carbon steel. It was found that increased volume fraction of the TiB2 reinforcement had not led to an appreciable increase in the wear resistance of the composite. The wear resistance of Al–10 Vf% TiB2 composite was found to exhibit a wear resistance 18.5 times higher than the unreinforced Al, whilst the Al–Cu–15 Vf% TiB2 composite was 3.1 times higher in resistance than unreinforced Al–Cu matrix. Replacement of the Al matrix with Al–Cu in the 15 Vf% composite did not improve the wear performance. The Al–15 Vf% TiB2 composite was shown to have almost the same wear resistance as plain carbon steel. Microstructural examination revealed that Al3Ti flakes gave way immediately to the crushing load during the wear process. However, the TiB2 particles resisted the wear process until rounded edges were configured.
The Arab Spring: The End of Postcolonialism
* Introduction: The Arab Spring: The End of Postcoloniality * 1. Decentering the World: How the Arab Spring Unfolded * 2. Towards Liberation Geography * 3. A New Language of Revolt * 4. Discovering a New World * 5. From the Green Movement to the Jasmine Revolutions * 6. The center cannot hold * 7. The End of Postcolonialism * 8. Race, Gender, and Class in Transnational Revolutions * 9. Libya: The Crucible * 10. Delayed Defiance * Conclusion. The People Demand the Overthrow of the Regime