Pressure/ friction welding of two metals

I am working on some soft metal thin film and wire, i.e. gold wire bonding to gold thin film. We all know that when two soft metals put
together, they may easily "bonded" to each other by simply applying some presurre.
Meanwhile, I need some more therectical background/mechanism of this "presurre welding" phenomenon. Would anyone give me some references and suggestions?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.