Housing assembly for rotary engine

A housing assembly for a rotary internal combustion engine, comprising:

• a rotor housing extending around an axis, the rotor housing having a peripheral inner face facing a rotor cavity, a first face at a first side and a second face at a second side opposite to the first side;
• a first side housing secured to the first side of the rotor housing, the first side housing defining a first inner side face facing the rotor cavity and the rotor housing;
• and
• a second side housing secured to the second side of the rotor housing, the second side housing defining a second inner side face facing the rotor cavity and the rotor housing, the rotor cavity bounded axially between the first side housing and the second side housing,
• one or more of the rotor housing, the first side housing, and the second side housing having:
• a main body made of a base material;
• and
• an external layer made of an alloy including the base material, a wear-resistance of the alloy greater than that of the base material, the external layer defining one or more of the first face of the rotor housing, the second face of the rotor housing, the first inner side face of the first side housing, and the second inner side face of the second side housing, the external layer including a transition layer extending from the main body, a ratio of a mass of the base material to a mass of the alloy by unit of volume gradually decreases within the transition layer from the main body.