Those who work in V-Ray versions lower than 3.1, be careful, in the materials in the BRDF section there is Microfaset GTR ( GGX ), if your version is older than 3.1, then the BRDF field will be empty. Choose Blinn, Phong or Ward - whatever suits you best. For Corona render, it is recommended to install a version of at least 1.5, since the glossiness of materials is configured with PBR in mind.