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May 23, 2022

Snatching Victory from the Jaws of Defeat part 1

There has not been that many updates for a while but that is hardly surprising when it is considered that the group has been consolidating data obtained from the DCF while working on sintering trials in time for the Plansee meeting for the end of May.

May has been a pivotal month for the cWC-RSB project. This month marks the first ever Generation 2 RSB sintered at Warwick, fulfilling the critical aim to showcase this work at Plansee 2022 - a highly strategic meeting for experts in W metal and cutting tools where the cWC-RSB project will meet its widest audience. Until the vacuum furnace got blown up that is - more on that later.

If there is one universal constant of experimental work is that failure is always an option. Whether it be the underpinning hypotheses, poor or inappropriate experimental design, personality clashes, equipment failure or too relevant now, war breaking out - whenever there is a long stretch of experimental work, there will be failure.

The key progress indicators are what the nature of the failures are and how they are responded to. This particular failure was equipment related and will be discussed in more detail in the next entry.

Prior to this, experimental work on RSB sintering trials had been progressing well. Recent results indicate that RSBs will expand to almost twice their volume prior to consolidation. Other results show that RSBs do not start to consolidate much before 1350oC. The 1300oC sintering trial is seen below:

RSB55 sintered at 1300C

RSB55 (target composition 30at% W, 30at% B, 30at% Fe, 7.5at% C and 2.5at% Cr) sintered at 3 hours at 1300oC.

Raising the sintering temperature to 1400oC for 2 hours had a dramatic change in the sintered RSB in that the sintered samples was observed to densify and shrink as for a generation 1 (Gen1) RSB55:

RSB55 sintered at 1400C for 2 hours

The Gen2 1400oC RSB55 is still not as dense as the original 1450oC vacuum sintered/SinterHIPPed RSB55 (86% vs 98% assuming similar phase presence) but is dense enough to be polished and considered a true Gen2 RSB. All that needs to be done is more trials at higher temperatures up to 1450oC.

That is until the vacuum furnace blew up, damaging the worktube and requiring the filing of a Near Miss Incident Report.

The basic cause of the failure was overpressuring the tube during the purge cycle - samples are vacuum sintered but an Ar purge is administered prior to pumpdown to remove trace O2 and water vapour from the tube and attain a decent vacuum - < 7 x 10-2 mbar (7 Pa) is a target for this vacuum furnace. However, the causes of the failure were not as simple as at first sight.

The next entry will look at methods used to identify the failure, the causes of said failure and how this inident can be used to better improve operator safety and furnace reliability in future.


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