LASER WELDING OF Ni_3Al INTERMETALLIC COMPUNDS FOILS

研究了首次研制成功的冷轧Ni_3Al箔的激光焊接性能。冷轧Ni_3Al箔的再结晶行为及力学性能的改善。在Ni_3Al重冷轧箔中发现了织构记忆效应：在晶粒长大过程中，再结晶织构恢复到原来的冷轧织构。我们发现，在晶粒长大过程中，韧性边界Σ1、Σ3和Σ9的比例增加，导致拉伸伸长率达到10%左右。激光点焊Ni_3Al箔冷轧箔在熔合区发生凝固开裂。在30 μm厚的箔片中，裂纹扩展不超过熔合区的收缩孔。而在100 μm厚的箔片中，裂纹通过热影响区传播到母材，但连续波激光的预热可以有效地抑制裂纹的扩展，这可能是由于热应力的降低。在再结晶箔的情况下不会发生凝固开裂。这是因为热影响区的塑性变形使热应力松弛。结果表明，冷轧箔和再结晶箔均可实现良好的激光点焊。激光焊缝焊接Ni_3Al箔采用直接二极管激光对冷轧和再结晶Ni_3Al箔的焊缝焊接行为进行了研究。厚度大于200 Km的冷轧薄板发生横向开裂，而厚度小于100 Km的薄板不发生横向开裂，这是因为产生的热应力较低。后者适用于再结晶箔。从而揭示了Ni_3Al箔的激光点焊和缝焊行为，以及良好的焊接条件，无焊缝开裂。

We studied laser welding properties of cold-rolled Ni_3Al foils which we for the first time successfully developed.1.Recrystallization behavior of cold-rolled Ni_3Al foils and improvement of the mechanical properties.We discovered a new phenomenon named texture memory effect in our heavily cold-rolled Ni_3Al foils : the recrystallization texture return to the original cold-rolled texture during grain growth. We found that the fraction of ductile boundaries, Σ1, Σ3, and Σ9, increases during grain growth, resulting in the large tensile elongation of about 10%.2.Laser spot welding of Ni_3Al foilsSolidification cracking occurs in the fusion zone in the case of cold-rolled foils. The cracks do not propagation far beyond the shrinkage hole of the fusion zone in the 30 μm-thick foils. In contrast they propagate through the heat-affected-zone to the base metal in the 100 μm-thick foils, but the crack propagation can be effectively suppressed by preheating with continuous wave laser, probably because of reduction of thermal stress.Solidification cracking does not occur in the case of recrystallized foils. It is because thermal stress is relaxed due to plastic deformation in the heat-affected zone.It is thus concluded that good laser spot welding is achievable for both cold-rolled and recrystallized foils.3.Laser seam welding of Ni_3Al foilsWe investigated the seam welding behavior of both cold-rolled and recrystallized foils by using direct diode laser. Transverse cracking occurs for the cold-rolled foils thicker than 200 Km, while not for the foils thinner than 100 Km because of low thermal stress generated. The latter goes for the recrystallized foils.We thus revealed the laser spot and seam welding behaviors of Ni_3Al foils and good welding conditions without weld cracking.