Improving Global Quality of Life
Improving Global Quality of Life
Improving Global Quality of Life
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4 Needs and challenges in welding and joining technologies<br />
<strong>of</strong> welding processes like electron beam (EB) welding and laser beam welding (LBW) which produce narrow<br />
weld metal and HAZ for joining these processes. Similarly, in the case <strong>of</strong> heat treatable Al alloys, use <strong>of</strong> the<br />
friction stir welding process can improve the properties <strong>of</strong> weld joints. Thus, one can observe a shift from<br />
conventional fusion welding processes to advanced and solid state processes in the case <strong>of</strong> these alloys<br />
developed by alloy and microstructural modification <strong>of</strong> the conventional structural materials.<br />
The testing and evaluation <strong>of</strong> weld joints <strong>of</strong> these materials would include structural integrity assessment<br />
and ageing management as these aspects are directly linked with safety <strong>of</strong> the plants or components using<br />
these alloys and conservation <strong>of</strong> the natural resources (by extending the life <strong>of</strong> the existing plants and<br />
components).<br />
Use <strong>of</strong> new structural materials like ceramics, composites and fibre-reinforced plastics necessitates joining<br />
them to themselves as well as to metals. None <strong>of</strong> the conventional welding processes are suitable for this<br />
purpose and one has to depend on processes like active brazing, adhesive joining, transient liquid phase<br />
(TLP) bonding etc. Weldability issues involved in these joints are considerably different from those present in<br />
welding <strong>of</strong> metals and alloys. Similarly, tests, characterisation and evaluation conducted on these joints for<br />
understanding the performance also differ considerably from those employed for conventional weld joints.<br />
The emphasis here is on the nature <strong>of</strong> the bond interface and strength <strong>of</strong> the joint, effect <strong>of</strong> thermal cycling,<br />
etc. unlike susceptibility to cracking in the case <strong>of</strong> welding <strong>of</strong> metals and alloys.<br />
Joining <strong>of</strong> advanced materials like bio-materials, electronic or magnetic or optical materials etc., throws up<br />
challenges that are not familiar to a conventional welding engineer or a materials scientist. Emphasis in this<br />
case shifts to preserving special physical properties like bio-compatibility, conductivity, magnetism etc. by<br />
employing micro-joining techniques, soldering and brazing. The processes and alloys chosen for soldering<br />
<strong>of</strong> semiconductor materials like Si differ considerably from those used in conventional soldering. Procedures<br />
like metallisation with layers <strong>of</strong> active elements like Cr or Ti and noble metal gold, and subsequent soldering<br />
using In-Bi alloys have been developed for joining Si wafers. In the case <strong>of</strong> bio-materials, encapsulation <strong>of</strong><br />
medication implants is an area where joining is a critical issue. Often, metals like Ti have to be joined to<br />
organic compounds like polyamide to produce a hermetically sealed joint. Low power laser beam joining<br />
techniques have been developed to produce bond width as low as 200 μm for these applications. Thus,<br />
one can see the science and technology <strong>of</strong> joining also has its share in the advances that take place in<br />
communication, electronics, information technology and biotechnology that have significantly improved<br />
the quality <strong>of</strong> life.<br />
Use <strong>of</strong> new joining techniques for new materials and applications brings to the fore the need for testing,<br />
characterisation and inspection <strong>of</strong> these joints. Often components or weld joints made <strong>of</strong> these materials and<br />
processes are so small that miniature specimens and testing devices have to be used for the determination<br />
<strong>of</strong> local properties and testing. Furthermore, these joints need to be characterised for their physical<br />
properties in addition to mechanical and chemical properties. Conventional non-destructive evaluation<br />
tools, developed and optimised for large metallic structures would be grossly inadequate in evaluating these<br />
micro-joints made from new materials and joining techniques. Hence, <strong>of</strong>ten new probes, techniques and<br />
standards have to be developed for their inspection.<br />
Furthermore, an increasing use <strong>of</strong> multi-material joints and life cycle extension techniques (including repair)<br />
<strong>of</strong> welded structures and components will represent key technologies for the future. This does not only<br />
require new interface design technologies where the assessment <strong>of</strong> the optimum weldability (joinability)<br />
and the evaluation <strong>of</strong> the service performance have to be linked much more closely, if both have to be<br />
assessed together. Careful evaluation <strong>of</strong> the interaction between selected materials, design and fabrication<br />
method, (see Figure 4.1), is one <strong>of</strong> the key factors towards a successful avoidance <strong>of</strong> failures <strong>of</strong> welded<br />
components in service. It is <strong>of</strong> particular interest to develop advanced test techniques to determine the local<br />
property gradient <strong>of</strong> such joints to understand the deformation behaviour and hence establish the design<br />
parameters better. Mechanical characterisation (including corrosion resistance) and flaw assessment <strong>of</strong> such<br />
hybrid joints are not a straightforward issue and still create challenges for the welding mechanics.<br />
Through Optimum Use and Innovation <strong>of</strong> Welding and Joining Technologies<br />
<strong>Improving</strong> <strong>Global</strong> <strong>Quality</strong> <strong>of</strong> <strong>Life</strong><br />
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