M.S. Li

Oxidation of Zr 2 (Al(Si)) 4 C 5 and Zr 3 (Al(Si)) 4 C 6 in air

The oxidation behavior of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) in air has been investigated. The oxidation kinetics of bulk Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) at 900-1300 degrees C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO(2), Al(2)O(3), and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) has been improved compared with Zr(2)Al(3)C(4), and is much better than Zr(3)[Al(Si)](4)C(6) to larger fraction of protective oxidation products, Al(2)O(3) and aluminosilicate/mullite.

Improving the high-temperature oxidation resistance of Zr2Al3C4 by silicon pack cementation

Silicon pack cementation has been applied to improve the oxidation resistance of Zr2Al3C4. The Si pack coating is mainly composed of an inner layer of ZrSi2 and SiC and an outer layer of Al2O3 at 1200 degrees C. The growth kinetics of silicide coating at 1000-1200 degrees C obey a parabolic law with an activation energy of 110.3 +/- 16.7 kJ/mol, which is controlled by inward diffusion of Si and outward diffusion of Al. Compared with Zr2Al3C4, the oxidation resistance of siliconized Zr2Al3C4 is greatly improved due to the formation of protective oxidation products, aluminosilicate glass, mullite, and ZrSiO4.

Simulations on Elastoplasticity of the Monolithic Aluminum Armature Under the Contact Force

Keeping good contact of the armature-rail interface (ARI) is essential for electromagnetic launch technology. To investigate the contact mechanism of ARI and improve the contact condition, the elastic-plastic deformation of the monolithic aluminum armature (MAA) under the contact force is analyzed. Contact force, contact area, and the distribution of contact pressure are calculated, and several kinds of armatures with different arm lengths are compared under the same conditions. The calculating loads include the pretightening force under the initial preload and the electromagnetic force from the pulse current. The simulation results show that both the contact force and the contact area under the plastic deformation are bigger than those under the elastic deformation, which is due to the higher spring-back force and displacement. A longer arm length can result in better flexibility and lower contact force. The effect of the electromagnetic force versus the contact force is increased with the arm length.

Design and Testing of a Two-Turn Electromagnetic Launcher

A multiturn railgun was designed to obtain high inductance gradient. It was made up of two pairs of copper rails. These two pairs were arranged up and down in space and were separated by the insulating structures. Each pair was an independent circuit with its own armature conductor. They were connected serially at the breech with a crossover. The two parallel armatures constitute the projectile with an insulating container. The bore size was 30 mm 60 mm. The rails were tightened with two pairs of insulating wedges against insulating spacers. Two up and down wedges constituted a frictional pair. The upper wedges would move down when the barrel containment was tightened gradually through the bolts, and they would produce enough preload to the rails to keep the gaps of each rail pair to 30 mm. The magnetic field in the barrel was simulated, and the mean inductance gradient was estimated to be 1.3 . The B-dot probes were also installed to diagnose the movement of the projectile in the barrel. Launch experiments with a peak current of 299 kA were conducted to test the performance of this two-turn electromagnetic launcher.