Laser Direct Metal Deposition of Dissimilar and Functionally graded alloys

Abstract

The challenges in the deposition of dissimilar materials are mainly related tothe large differences in the physical and chemical properties of the depositedand substrate materials. These differences readily cause residual stresses andintermetallic phases. This has led to the development of functionally gradedmaterials which exhibit spatial variation in composition. Laser direct metaldeposition due to its flexibility, it offers wide variety of dissimilar andfunctionally graded materials deposition.Despite considerable advances in process optimization, there is a ratherlimited understanding of the role of metallurgical factors in the laserdeposition of dissimilar and functionally graded alloys. The aim of this workis to understand and explain mechanisms occurring in diode laser depositionof dissimilar materials and functionally graded materials. The first part ofthis work addressed diode laser deposition of Inconel 718 nickel alloy to Ti-6Al-4V titanium alloy. Here, the effect of laser pulse parameters and powdermass flow rates on the stress formation and cracking has evaluated byexperiment and numerical techniques. Results showed that the cladthickness was an important factor affecting the cracking behaviour. In thesecond part of this study, an image analysis technique has been developed tomeasure the surface disturbance and the melt pool cross section size duringlaser direct metal deposition of Inconel 718 on a Ti-6Al-4V thin wall. It wasnoted that under tested conditions the overall melt pool area increased withthe increase in powder flow rate; the powder carrier gas flow rates alsoseemed to play important roles in determining the melt pool size. In thethird part of this study, a parametric study on the development of Inconel718 and Stainless steel 316L continuously graded structure has been carriedout. Results suggested that microstructure and other mechanical propertiescan be selectively controlled across the deposited wall.The results presented in this dissertation can be used as a metallurgical basisfor further development of dissimilar and functionally gradedmanufacturing using LDMD technique, guiding future manufacturingengineers to produce structurally sound and microstructurally desirablelaser deposited samples.

Date of Award	1 Aug 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lin Li (Supervisor)