The document discusses nickel-based super alloys, including their properties, applications, common alloying elements, and weldability issues. Super alloys exhibit excellent mechanical strength and creep resistance at high temperatures due to their face-centered cubic crystal structure and alloying with nickel, cobalt, chromium, and other elements. Weldability problems with nickel alloys include hot cracking caused by sulfur and porosity caused by nitrogen, which require careful control of welding parameters.