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Effect of Interstitial Elements on the Welding of Selective Laser Melted Stainless Steel Alloys
WEBVTT Kind: captions Language: en
00:00:00.800 you 00:00:09.92000:00:09.930 yeah so as he said I'll be talking about 00:00:12.50000:00:12.510 the effect of interstitial elements on 00:00:14.29900:00:14.309 the welding of selectively laser melted 00:00:17.33000:00:17.340 304 l so this this work is also 00:00:20.72000:00:20.730 conducted through the NSF iucrc magic 00:00:23.90000:00:23.910 program and is also sponsored by Los 00:00:26.63000:00:26.640 Alamos National Lab so it actually 00:00:28.40000:00:28.410 complements Brandon's Brandon's work 00:00:31.90900:00:31.919 quite well but we're more focused on is 00:00:34.97000:00:34.980 once we get a good build what happens if 00:00:38.51000:00:38.520 you weld it you're essentially putting 00:00:40.46000:00:40.470 this large macro scale weld on all these 00:00:42.92000:00:42.930 small micro scale welds and how does 00:00:45.80000:00:45.810 that affect the weldability in the end 00:00:47.75000:00:47.760 and you're cracking susceptibility so 00:00:51.91000:00:51.920 our overall goal of this project is to 00:00:56.09000:00:56.100 determine the fundamental differences in 00:00:58.51000:00:58.520 in both gas tungsten arc welding but 00:01:01.13000:01:01.140 also other processes as well for this 00:01:03.29000:01:03.300 talk will focus on gas tungsten arc 00:01:05.03000:01:05.040 welding selectively laser melted 304 L 00:01:09.41000:01:09.420 and compare that to conventionally 00:01:11.06000:01:11.070 produce 304 L and more specifically how 00:01:15.17000:01:15.180 did how does the change in interstitial 00:01:17.12000:01:17.130 elemental distribution and Composition 00:01:19.67000:01:19.680 affect the weldability in that sense so 00:01:23.69000:01:23.700 on the right we have a typical 304 L a 00:01:27.86000:01:27.870 rot composition was put into thermo-calc 00:01:31.01000:01:31.020 and you can see it's your your typical 00:01:34.00000:01:34.010 get your delta ferrite forming first and 00:01:36.74000:01:36.750 then austenitic structure at the end so 00:01:41.28900:01:41.299 when we when we effectively changed 00:01:44.71900:01:44.729 these carbon nitrogen sulfur phosphorus 00:01:47.24000:01:47.250 which typically affect the weldability 00:01:49.99000:01:50.000 and now with the 304 l produced by SL m 00:01:55.82000:01:55.830 with all the powder metallurgy you pick 00:01:58.13000:01:58.140 up a lot of oxygen so now we effectively 00:02:00.46900:02:00.479 change our oxygen content and well as 00:02:02.12000:02:02.130 well and we see that this this graph or 00:02:06.98000:02:06.990 this Showell simulation plot essentially 00:02:10.75900:02:10.769 changes and starts to form these panels 00:02:12.92000:02:12.930 at higher temperatures and eventually 00:02:15.19900:02:15.209 set up solidifies these manganese 00:02:17.18000:02:17.190 silicate slags 00:02:18.84000:02:18.850 towards the end and where do those 00:02:21.72000:02:21.730 distribute and how do they have 00:02:23.85000:02:23.860 essentially affect the weldability the 00:02:25.65000:02:25.660 cracking susceptibility in the end so 00:02:28.92000:02:28.930 what we did we took some non cracked 304 00:02:33.27000:02:33.280 L samples made on it yes M to 90 so 00:02:37.26000:02:37.270 these were done with virgin powder so we 00:02:39.57000:02:39.580 tried to minimize the amount of oxygen 00:02:41.27000:02:41.280 and then what we did was we stress 00:02:43.83000:02:43.840 relieved them for tense at 10 65 for 30 00:02:47.34000:02:47.350 minutes as per ms 275 9 and so the 00:02:54.21000:02:54.220 reason we did that was to eliminate the 00:02:56.16000:02:56.170 effect of residual stress because these 00:02:58.14000:02:58.150 parts typically have a much higher 00:03:00.15000:03:00.160 degree of residual stress than the raw 00:03:01.68000:03:01.690 product so we didn't want that to affect 00:03:03.12000:03:03.130 the the cracking behavior as we 00:03:06.57000:03:06.580 previously saw so we we heat treated 00:03:09.09000:03:09.100 these and then afterwards they were 00:03:10.50000:03:10.510 machined down to our sample geometry and 00:03:14.03000:03:14.040 TJ welded and Sigma jig fixture with 00:03:19.32000:03:19.330 ranging amounts of stress from 0 to 20 00:03:23.43000:03:23.440 ksi so for those of you that aren't 00:03:27.78000:03:27.790 familiar with the Sigma tech test is a 00:03:30.03000:03:30.040 quite old test from the 80s and it's 00:03:35.16000:03:35.170 actually hot cracking susceptibility 00:03:36.81000:03:36.820 test which you apply of pre-loaded 00:03:40.32000:03:40.330 stress onto the sample and perform the 00:03:43.17000:03:43.180 welding under the stress to try to 00:03:45.36000:03:45.370 induce the cracking and your cracking 00:03:47.70000:03:47.710 susceptibility is depending on how much 00:03:49.68000:03:49.690 stress you need to apply that to induce 00:03:51.60000:03:51.610 the cracking so this can this is a good 00:03:54.96000:03:54.970 test for comparing compositional 00:03:57.15000:03:57.160 variations in between materials so we we 00:04:01.14000:04:01.150 chose this one as a way to to try to 00:04:05.45000:04:05.460 determine these differences between the 00:04:07.83000:04:07.840 am and rock materials so just to give 00:04:11.61000:04:11.620 you a little bit about the the material 00:04:13.29000:04:13.300 specifications and the differences in 00:04:14.85000:04:14.860 composition what we saw was with the the 00:04:18.30000:04:18.310 SLM we built these samples in two 00:04:21.63000:04:21.640 different directions so we built them in 00:04:23.94000:04:23.950 the vertical direction and we also built 00:04:26.46000:04:26.470 them in the horizontal direction which 00:04:27.96000:04:27.970 I'll show you schematic in a slider to 00:04:32.14000:04:32.150 and then we also have our rot material 00:04:34.21000:04:34.220 there you can see that there's actually 00:04:35.50000:04:35.510 quite a bit of carving and the rot 00:04:37.87000:04:37.880 material compared to the to the to the 00:04:41.46900:04:41.479 am material but in the end the chrome 00:04:44.86000:04:44.870 and nickel equivalencies are quite 00:04:46.21000:04:46.220 similar and you see the chrome and 00:04:48.28000:04:48.290 nickel equivalencies both indicate that 00:04:51.43000:04:51.440 we'll have a primary ferrite plus 00:04:52.75000:04:52.760 Austinites location mode upon welding 00:04:54.85000:04:54.860 and then the major difference that we 00:04:57.61000:04:57.620 see here is not actually the nitrogen 00:04:59.37900:04:59.389 which I was expecting since these were 00:05:01.03000:05:01.040 all built under nitrogen and atomized in 00:05:03.64000:05:03.650 nitrogen the nitrogen they're actually 00:05:06.07000:05:06.080 quite a little bit higher in the Sprott 00:05:08.50000:05:08.510 material but we actually see a tenfold 00:05:13.00000:05:13.010 increase of the oxygen content in the 00:05:15.49000:05:15.500 what in the am material compared to the 00:05:17.80000:05:17.810 rock material so we want to see how that 00:05:20.50000:05:20.510 how how these specific particular 00:05:22.62900:05:22.639 elements might affect the cracking the 00:05:27.01000:05:27.020 am atmosphere was under nitrogen as well 00:05:29.70000:05:29.710 and we didn't see a significant jump 00:05:33.64000:05:33.650 spike in the 00:05:39.26000:05:39.270 not in a significant amount of nitrogen 00:05:41.85000:05:41.860 no so just show you a little bit about 00:05:51.30000:05:51.310 the the weld what the weld geometry look 00:05:54.72000:05:54.730 like we have a typical GTA weld this is 00:05:57.33000:05:57.340 a two millimeter thick rot material and 00:06:00.18000:06:00.190 what we do see is this is this skeletal 00:06:04.86000:06:04.870 ferrite with the mixture of laughy 00:06:07.62000:06:07.630 ferrite so we do indicate a primary 00:06:09.90000:06:09.910 ferrite plus austenite structure so the 00:06:13.59000:06:13.600 WRC predicted quite well 00:06:15.84000:06:15.850 and we saw that it was it was clean very 00:06:20.13000:06:20.140 well conducted weld and one thing I do 00:06:22.65000:06:22.660 want to note because this is important 00:06:24.36000:06:24.370 for later as we do not see excessive 00:06:26.82000:06:26.830 oxidation of the surface or the route we 00:06:29.82000:06:29.830 shielded this with UHP argon both on the 00:06:32.82000:06:32.830 surface and had a back trail back 00:06:35.13000:06:35.140 shielding on the root surface as well so 00:06:38.16000:06:38.170 we try to keep this as clean as possible 00:06:39.93000:06:39.940 as to not introduce any extra oxygen 00:06:41.94000:06:41.950 that might skew the results and then so 00:06:48.06000:06:48.070 when we did the Sigma jig testing of the 00:06:49.74000:06:49.750 wrought 304 L we see a typical fracture 00:06:54.33000:06:54.340 pattern as we slowly increase the stress 00:06:56.94000:06:56.950 I must note that these signatures 00:07:00.03000:07:00.040 samples the the sample geometry was 00:07:03.11000:07:03.120 slightly sub sized just because that was 00:07:06.63000:07:06.640 the build volume that we had for the 00:07:08.40000:07:08.410 a.m. samples so we had to match 00:07:10.47000:07:10.480 everything to make it the most 00:07:12.27000:07:12.280 consistent but we see a slow progression 00:07:14.76000:07:14.770 of cracking down the centerline as we 00:07:18.06000:07:18.070 increase the stresses until we finally 00:07:20.58000:07:20.590 fracture it at 30 ksi and this I believe 00:07:23.43000:07:23.440 is due to edge effects since we had a 00:07:26.31000:07:26.320 small smaller sample than the normal 00:07:28.86000:07:28.870 Sigma jig as far as width goes so it's 00:07:32.82000:07:32.830 very characteristic of a 304 L nothing 00:07:34.92000:07:34.930 out of the ordinary 00:07:36.33000:07:36.340 we had very clean fracture surfaces and 00:07:39.77000:07:39.780 nothing nothing to cause any alarm so 00:07:44.43000:07:44.440 then we look at our AM welds so here's a 00:07:48.63000:07:48.640 schematic of our of our a and Bill's 00:07:51.33000:07:51.340 both in the horse 00:07:52.35000:07:52.360 donal direction on the bottom and built 00:07:54.17900:07:54.189 in the vertical direction on top you 00:07:56.30900:07:56.319 can't see a change in the weld 00:07:59.67000:07:59.680 morphology and this could be a product 00:08:03.77900:08:03.789 of of where where this was cross section 00:08:07.08000:08:07.090 in the weld this could also be a product 00:08:09.11900:08:09.129 of compositional variations through the 00:08:12.77900:08:12.789 build as they were built in different 00:08:14.04000:08:14.050 directions so but that that didn't that 00:08:19.37900:08:19.389 didn't necessarily change the fracture 00:08:21.89900:08:21.909 behavior between the two different sets 00:08:24.02900:08:24.039 of samples and since they were heat 00:08:25.74000:08:25.750 treated they were more uniform than in 00:08:29.30900:08:29.319 the asbill but what we did see where 00:08:31.55900:08:31.569 small silicate islands in the builds 00:08:33.42000:08:33.430 themselves so we think that these the 00:08:37.62000:08:37.630 silicate islands are typically start out 00:08:39.87000:08:39.880 much smaller and make whoreson during 00:08:41.88000:08:41.890 heat treatment but we did see a 00:08:44.56900:08:44.579 scattering of these small silicates that 00:08:46.80000:08:46.810 you can see in the image on the left and 00:08:49.17000:08:49.180 in the weld you can see towards the top 00:08:52.41000:08:52.420 is the or so through the middle as a 00:08:54.99000:08:55.000 fusion line and towards the top you see 00:08:56.99000:08:57.000 primary ferrite it's a skeletal ferrite 00:09:00.00000:09:00.010 solidification so we get primary ferrite 00:09:02.49000:09:02.500 plus austenite which was also predicted 00:09:04.35000:09:04.360 through the WRC so that's all good but 00:09:07.88900:09:07.899 what we did see was a large degree of 00:09:10.82900:09:10.839 porosity and defects all over the 00:09:12.81000:09:12.820 material so here on the left you see 00:09:16.49000:09:16.500 indications of possible ductility 00:09:18.72000:09:18.730 cracking and you see a large amounts of 00:09:21.42000:09:21.430 porosity coming to the surface in some 00:09:24.24000:09:24.250 cases so you can see on the right of 00:09:25.86000:09:25.870 that left image there's a darker region 00:09:29.18900:09:29.199 and that's actually an oxide layer that 00:09:31.76900:09:31.779 had not come off this oxide layer had 00:09:33.96000:09:33.970 had sort of flaked off but that sort of 00:09:37.68000:09:37.690 covers up some of the subsurface pores 00:09:39.66000:09:39.670 that we saw near the surface and then we 00:09:42.81000:09:42.820 also saw near the towline we're seeing 00:09:44.81900:09:44.829 the segregation of the silicate that was 00:09:46.76900:09:46.779 flowing to the towline and forming these 00:09:48.93000:09:48.940 silicate islands with a mixture of 00:09:51.30000:09:51.310 spinel in them as well and so we're 00:09:54.03000:09:54.040 seeing these just decorating the towline 00:09:56.18900:09:56.199 on either side of the weld four and this 00:09:59.55000:09:59.560 was consistent throughout all of the 00:10:01.05000:10:01.060 welds 00:10:03.96000:10:03.970 and then what we also saw we observed we 00:10:08.49000:10:08.500 have sort of the silicate formation also 00:10:10.47000:10:10.480 on the root of the weld so we see this 00:10:13.71000:10:13.720 thin film in these samples and you can 00:10:17.28000:10:17.290 also see that the actual towline of the 00:10:19.74000:10:19.750 weld is a little bit jagged and full of 00:10:23.73000:10:23.740 these oxide particles and we did again 00:10:26.97000:10:26.980 use back shielding in argon to try to 00:10:30.63000:10:30.640 minimize any oxygen and pick up from the 00:10:33.21000:10:33.220 atmosphere so we didn't oxidize these 00:10:35.79000:10:35.800 surfaces and this was done under the 00:10:37.98000:10:37.990 same setup as the raw material so I'm 00:10:40.59000:10:40.600 very very different at just macroscale 00:10:43.26000:10:43.270 characteristics that we saw on the 00:10:44.82000:10:44.830 surface now when we started applying 00:10:47.76000:10:47.770 loads you see that there's some 00:10:51.60000:10:51.610 different oxides on the surface but this 00:10:54.72000:10:54.730 was an unloaded sample there was no 00:10:57.93000:10:57.940 observed cracking as we started 00:11:00.66000:11:00.670 increasing the the loads on our turn 00:11:04.74000:11:04.750 welding we started seeing evidence that 00:11:06.93000:11:06.940 we may have ductility dip cracking in 00:11:08.85000:11:08.860 the weld and then we saw a full fracture 00:11:13.77000:11:13.780 with quite a bit of oxides along the 00:11:16.59000:11:16.600 fracture line so you can see there in 00:11:18.75000:11:18.760 the middle there's there's dendrites on 00:11:21.27000:11:21.280 either side and there's a sort of a 00:11:23.46000:11:23.470 sharp region where it's a little bit 00:11:25.62000:11:25.630 darker and with spa EDS analysis we 00:11:29.37000:11:29.380 indicate high amounts of oxygen content 00:11:31.52000:11:31.530 manganese and silicon so we saw we saw 00:11:35.19000:11:35.200 quite a bit of that happening in the 00:11:36.84000:11:36.850 weld and I'll show you some more images 00:11:38.67000:11:38.680 on that later and we also observed that 00:11:41.16000:11:41.170 we had premature and premature 00:11:42.63000:11:42.640 separations so we only got to 20 ksi 00:11:45.06000:11:45.070 before these fully fractured so so there 00:11:50.28000:11:50.290 are quite a few differences there we 00:11:52.23000:11:52.240 also saw on the surface you could see 00:11:55.11000:11:55.120 these small dark speckled regions around 00:11:57.33000:11:57.340 these cracks and those are actually 00:11:59.73000:11:59.740 these little silicates that had I don't 00:12:02.94000:12:02.950 know if they had vaporize on the surface 00:12:04.53000:12:04.540 or had you know sort of floated to the 00:12:06.78000:12:06.790 surface on these cracks and then we see 00:12:09.57000:12:09.580 evidence of migrated grain boundaries 00:12:11.10000:12:11.110 which is why we believe this may be 00:12:13.01000:12:13.020 ductility dipped cracking occur 00:12:15.36900:12:15.379 I mean so along the fracture surfaces we 00:12:20.61900:12:20.629 see these silicate films and you also 00:12:22.21000:12:22.220 see these large silicate particles that 00:12:26.28900:12:26.299 are quite irregular and maybe sites of 00:12:28.83900:12:28.849 initiation for a fracture for premature 00:12:31.92900:12:31.939 fracture and then we also see an oxide 00:12:33.87900:12:33.889 coating you could sort of see a dark 00:12:35.55900:12:35.569 sheen on the right-hand image an oxide 00:12:38.34900:12:38.359 coating on the dendrites themselves 00:12:40.41900:12:40.429 along the centerline of the fusion the 00:12:44.82900:12:44.839 centerline of the weld I'm sorry so we 00:12:47.64900:12:47.659 think this may be ductility dipped 00:12:49.17900:12:49.189 cracking Knisley is published a paper on 00:12:54.23900:12:54.249 the the presence of oxygen and super 00:12:57.21900:12:57.229 alloys in nickel super alloys may cause 00:13:01.82900:13:01.839 an increase in ductility dipped cracking 00:13:04.47900:13:04.489 but it wasn't quantified and this effect 00:13:06.96900:13:06.979 has not been studied another another 00:13:09.18900:13:09.199 sample so we think that this might be 00:13:12.72900:13:12.739 since we're under high restraint we 00:13:14.94900:13:14.959 think this might be a product of 00:13:17.82900:13:17.839 ductility dipped cracking for some of 00:13:21.09900:13:21.109 those some of the fracture mechanisms as 00:13:23.88900:13:23.899 well as solidification cracking at 00:13:25.59900:13:25.609 higher and higher stresses so that's 00:13:28.74900:13:28.759 something that we need to look into 00:13:30.50900:13:30.519 quite a bit more and since we have these 00:13:33.42900:13:33.439 high these oxidizing elements such as 00:13:37.26900:13:37.279 manganese silicon and Chrome they tend 00:13:40.05900:13:40.069 to pick up all that extra oxygen and as 00:13:43.11900:13:43.129 well we already have these silicate 00:13:44.59000:13:44.600 particles in them in the sample itself 00:13:47.22900:13:47.239 before we weld so we might just be 00:13:48.99900:13:49.009 redistribute them into the weld and 00:13:52.37900:13:52.389 forming these cracking initiation sites 00:13:56.24900:13:56.259 so to conclude the the oxygen inherent 00:13:59.07900:13:59.089 to the the 3d printing process it may 00:14:01.92900:14:01.939 pose a detrimental effect to a 00:14:06.89900:14:06.909 detrimental occurrence of cracking 00:14:09.68900:14:09.699 premature cracking compared to the 00:14:11.91900:14:11.929 wrought material we do need is a study 00:14:14.58900:14:14.599 this quite a bit more and figure out 00:14:16.53900:14:16.549 exactly what's happening and if this was 00:14:19.02900:14:19.039 a product of these builds themselves or 00:14:21.00900:14:21.019 if this is a product of other batches of 00:14:23.01900:14:23.029 builds and also study other other 00:14:29.32900:14:29.339 types of welding to compare this 00:14:31.44900:14:31.459 phenomena and we did see an increase of 00:14:34.97000:14:34.980 cracking susceptibility between these 00:14:36.80000:14:36.810 SLM samples compared to the rot so I 00:14:39.19900:14:39.209 think this is definitely an issue that 00:14:40.81900:14:40.829 needs to be addressed and looked into 00:14:42.88900:14:42.899 quite a bit more and determine what 00:14:46.24900:14:46.259 these act these mechanisms actually are 00:14:48.25900:14:48.269 causing this premature failure 00:14:52.72000:14:52.730 [Applause]
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