$3.$ Friction welding is environmentally friendly, as it does not produce $\_$ or require $\_$ materials, making it preferable for green manufacturing processes. $($True$/$False$)$

$4.$ Forge welding is limited to ferrous metals due to the requirement for $\_\_\_$ at high temperatures, which can be difficult to achieve with non$-$ferrous metals. $($True$/$False$)$