weld metal 外延生长 uoisny Cu 詈 Grain (crystal) base metal (a) GB1 GB2 weld metal m Base Metal Weld Pool GB 1 (substrate) (liquid) base 6u!pleM (b) metal 100μm GB 2 FL resolidified zone Al Epitaxial Stainless Steel Growth 20μm外延生长 Cu Al Stainless Steel