1. Major challenges in TIG welding of titanium
MICROSTRUCTURE AND MECHANICAL ANALYSIS OF TIG WELDED JOINT BETWEEN Ti6Al4V AND COMMERCIALLY PURE TITANIUM Deepak Kumar, Dr. Mohd. Zaheer Khan Yusufzai Department of Mechanical Engineering, Indian Institute of Technology (BHU), Varanasi
Need for the Study
Working parameters
Conclusions
Parameters
Specimen 1
Specimen 2
Specimen 3
Welding Current ( A )
192
202
216
Welding Voltage ( V ) 20
Welding Speed ( mm/sec ) 2 3 4
Current type
DCSP
Electrode diameter ( mm )
2.4
Surface discoloration gives a good indication of the degree of atmospheric contamination. Under perfect shielding conditions the weld is bright and silvery in appearance. Discoloration at the outer edges of the HAZ is not generally significant and may be ignored. As contamination increases the color changes from silver to a light straw color, then dark brown, dark blue, light blue, grey and finally a powdery white.
As heat input increases, the fusion zone and HAZ area also increase. Significant grain coarsening is found in the HAZs of all the joints.
Extent of grain coarsening increases with increasing heat input. Near to the fusion boundary the size of the grains in the HAZ of the joints is found to be relatively coarser at high heat input and finer at low heat input.
A significant grain coarsening size is noticed in the fusion zone which consists of parallel alpha cells in different orientation bounded by beta phase and in HAZ, equiaxed grains had grown larger in size compared to grains in base metal .As a result, the degree of grain coarsening decreases as one move from the fusion zone to the base metal.
Titanium and its alloys are one of the most widely used groups of material in engineering applications, and a lot of improvement is needed in the area of its welding.
Titanium grade 9 alloy which is compromise between both of these alloys but is very costly and used in aerospace industry. So, welding of these two alloy together can be a substitute for titanium grade 9 alloy.
Results
Width of weld bead (Front) ( mm )
Width of weld bead (Back) (mm)
Color of weld bead
Area of fusion zone ( inch2 )
Specimen 1 15 7
Silver
0.04
Specimen 2 13 5
Brown
0.03
Specimen 3 11
0.02
Major challenges in TIG welding of titanium
Titanium is a reactive metal; it burns in pure oxygen at 600°C and in nitrogen at around 800°C. Oxygen and nitrogen also diffuses into titanium at temperatures above 400°C raising the tensile strength but embrittling the metals.
In the form of a powder or metal shavings titanium also constitutes a fire hazard.
The drawbacks of GTAW are the high heat input leading to distortion, porosity from trapped shielding gases and low welding speeds due to the limited power of the torch and wide arc leading to low penetration.
Tabular representation of results obtained from welded joint
Image representing preparation of sample for metallographic study from welded joint
Approach/Methods
Optical microscopic image of Ti6Al4V
Optical microscopic image of CP Titanium
Specimens of both alloys are cut in dimension of 100mm*50mm*3mm.
Before welding all the edges are thoroughly cleaned mechanically and chemically in order to avoid any source of contamination like rust, scale, dust, oil, moisture etc.
After tackling the sheets together, titanium sheets are welded by TIG welding in butt joint along longitudinal direction using TIG welding machine with air cooled torch head, (SUPRA TIG 400). Numerical control unit is used for controlling the travel speed.
Macroscopic image of welded specimen
Fusion zone
CP Titanium
Ti6Al4V
Future Scope
Ductility of welded zone decreases compared to base metal which is not desirable so a suitable filler metal having proper compatibility with these two metals can be used to increase its ductility.
Optical microscopic image of indicated parts of fusion zone
References
A.B. Short et. al, Gas tungsten arc welding of α+β titanium alloys: a review. Material Science and Technology. Volume 25, Issue 3, , (2009)
A. Karpagaraj, N. Sivashanmugam, K. Sankaranarayansamay, Some studies on mechanical properties and microstructural characterization of automated TIG welding of thin commercially pure titanium sheets. Materials Science & Engineering. Volume A640, , (2015)
Experimental Set-up