A method of additive manufacturing and heat treatment. A substrate is secured to a fixture and an additive manufacturing system is operated to perform a build process by building a part on the substrate secured to the fixture, the part being built by forming a series of layers of metallic material on the substrate, the metallic material melting and solidifying during the build process thereby bonding the part to the substrate and creating thermally induced stress in the part. The part, the substrate and the fixture are moved together from the additive manufacturing system to a heat treatment system, wherein the substrate remains secured to the fixture and the part remains bonded to the substrate as they are moved. The heat treatment system is operated to perform a heat treatment process by heating the part, the substrate and the fixture together thereby relieving the thermally induced stress in the part, the substrate remaining secured to the fixture during the heat treatment process. Finally the substrate is released from the fixture and the part and the substrate are removed from the fixture. The part remains bonded to the support as they are removed from the fixture.