Effect Of Heat Treatment On Microstructure Of Nickel-base . - EWI
Effect of Heat Treatment on Microstructureof Nickel-base Superalloyfabricated by Laser-Powder Bed FusionAdditive ManufacturingHyeyun Song and Prof. Wei ZhangThe Ohio State UniversityDr. Shawn M. KellyEWI1NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Outlines1. Objectives2. As-built samples produced by L-PBF AM Characteristics of microstructures Confirmation of precipitates Effect of support on hardness value3. Post-build heat treatment Homogenization Aging4. Effect of heat treatment on microstructure5. Effect of heat treatment on surface oxidation6. Results and future works2NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Objectives Additive manufacturing (AM) is advantageous for direct production of complex shapedcomponents based on three-dimensional CAD. Requirements for better qualification of parts built by laser powder bed fusion:- Understanding of microstructures due to a large number of repeated heating and cooling cycles- Understanding of the effect of post-build heat treatment on microstructures and propertiesApproaches used Two groups of IN718 samples:- Built either directly on substrate or with a grid support- 375 layers in building direction to a height of 15 mm- As-built dimensions fairly accurate15mm5mm3NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Outlines1. Objectives2. As-built samples produced by L-PBF AM Characteristics of microstructures Confirmation of precipitates Effect of support on hardness value3. Post-build heat treatment Homogenization Aging4. Effect of heat treatment on microstructure5. Effect of heat treatment on surface oxidation6. Results and future works4NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Microstructure of as-built sample Size of bright precipitates: 500 800 nm Dendrite Arm Spacing (DAS) ofgray matrix: 1 1.8μm Bright regions are enriched in Nb, Mo and Ti and depleted in Cr, Fe and Ni. The chemical composition matches that of Laves phase. NbC and delta, two other common precipitates, were not observed.5NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Diffraction patterns ofFCC matrix and Laves phaseB Z [011]-200 -11-154.74⁰-1-11 AMatrix: FCCB1-1170.52⁰11-1200Matrix: FCC; a 0.36 nmLaves phase: HCPB Z [0001]01-1060⁰-1100 60⁰-20-2-2-20-10106NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplications0000A0-11010-101-10002-2Laves: HCP; a 0.48, c 0.74 nmAxial0-22ratio c/a 1.54220CIMJSEA202
Effect of the support on the hardness valueHardness map of sample without supportHardness map of sample with supportAvg.316Avg.301Max.344Max.337Min.290Min.271 Small reduction (5%) in hardness value of the sample with support7NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Correlation of hardness variation and Laves phaseAvg. fraction of Laves phaseWithout support: 2.62%With support: 2.64%2.81% volume fraction of Laves phase in the highest hardness region Larger fraction and coarser size of Laves phase isa likely factor for the higher hardness locally.1.68% volume fraction of Laves phase in the lowest hardness region8NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Outlines1. Objectives2. As-built samples produced by L-PBF AM Characteristics of microstructures Confirmation of precipitates Effect of support on hardness value3. Post-build heat treatment Homogenization Aging4. Effect of heat treatment on microstructure5. Effect of heat treatment on surface oxidation6. Results and future works9NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Post-built heat treatment As-built microstructure does not have γ” and γ’, the important strengtheningprecipitates for IN718. Hence, post-built heat treatment is still required. Two commonly used standards are:ScheduleHomogenizationSolutionannealAgingAMS 2773E –Casting1093 C for 2hours, AC982 C for 1hour, AC718 C for 8 hours, FC to 621 C, hold for atotal precipitation time of 18 hrsAMS 2774D –WroughtN/A954 C for 1hour, AC10 hours at 760 C, FC to 649 C and holdfor 20 hrs total precipitation time, ACAMS – Aerospace Materials Specification; AC – Air cooling; FC – Furnace cooling. AMS 2773E was studied at first, since the as-built microstructure is expected to becloser to cast than wrought. Questions to be answered: Can Laves phase be completely dissolved after homogenization? What effect does the cooling rate for homogenization have? Is the solution step necessary?10NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Group 1: Homogenization (and no solution annealing)1. Peak temperature: 1100 ⁰C or 1200 ⁰C (above Laves and δ solvus temperatures)2. Heating rate: 5 ⁰C/min2 or 8 hours1100⁰C3. Cooling:Various coolingor Air cooling1200⁰C Force air cooling5 ⁰C/min Water quenchingHomogenization4. Shielding gas for heating and holding steps: Ar (0.97 liter per min)Group 2: Casting AMS 2773E (homogenization solution)1 hour1. Homogenization at 1093 C for 2982⁰Chours, ACAir cooling2. Solution:5 ⁰C/min Heating rate: 5 ⁰C/minSolution Peak temperature: 982⁰C Shielding gas for heating and holding steps: Ar (0.97 liter per min)NSF I/UCRC Center Air coolingfor Integrative11Materials JoiningScience for EnergyApplicationsCIMJSEA
Microstructure after homogenization1100⁰C 2hrs Air coolingCooling rate: 2.4⁰C/s1100⁰C 2hrs Forced air coolingCooling rate: 5.3⁰C/s1100⁰C 2hrs Water quenchingCooling rate: 414⁰C/s Remaining Laves phase along the grain boundariesCasting: 1093⁰C 2hrs Air cooling982⁰C 1hr Air coolingNSF I/UCRC Center121200⁰C 8hrs Water quenchingCIMJSEAGrain growth & reduction of Laves phasefor IntegrativeNeedle-shapeddelta phase formedMaterials JoiningScience for Energyafter the solutionannealing stepApplications
Condition for aging Followed AMS (2773E) standard for casting condition:1. Homogenization: Holding at 1093⁰C for 2hours and air cooling2. Aging: Holding at 718⁰C for 8 hours and then furnace cooling 621⁰C for 10 hours (including cooling time from 718⁰C to 621⁰C)3. Shielding gas for heating and holding steps: Ar (0.97 liter per min)2 hour1093⁰CAir cooling718 ⁰C621 ⁰CFurnace cooling8 hours13NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplications10 hoursCIMJSEACooling in Ar
TEM images of aged sampleγ'γ''γ' Distinct morphology of newprecipitates formed after aging Evenly distribution of small poreswith avg. diameter of 41.5 nmGroup 1 sample: homogenization(and no solution annealing)14NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplications Avg. diameter of small precipitates (γ”):13.5 nm Avg. aspect ratio for large precipitates(γ’): 0.23 γ’: Ni3(Ti,Al), FCC, spherical or cubic γ’’: Ni3Nb, BCT, disk-shapedCIMJSEA
High resolution EDS analysis for aged sampleNb, Al γ’: Ni3(Ti,Al), FCC, spherical or cubic γ’’: Ni3Nb, BCT, disk-shaped15NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Outlines1. Objectives2. As-built samples produced by L-PBF AM Characteristics of microstructures Confirmation of precipitates Effect of support on hardness value3. Post-build heat treatment Homogenization Aging4. Effect of heat treatment on microstructure5. Effect of heat treatment on surface oxidation6. Results and future works16NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
As-built1100⁰C 2hrs1100⁰C 2hr ACCooling rate: 2.4⁰C/s1100⁰C 8hrs1200⁰C 2hrs1200⁰C 8hr ACCooling rate: 2.4⁰C/s1200⁰C 8hrs Casting Aged WroughtCasting(1093⁰C 2hrs AC 982⁰C 1hr AC)Potential factors for hardness change:NSF I/UCRC Centerfor Integrative Microstructure:Precipitates (i.e., Laves phase & delta) and grain sizeMaterials Joiningfor EnergyCompositionalhomogeneity17 Chemistry:ScienceApplicationsCIMJSEA
EBSD results showing grain growthAs-built1100⁰C, 8hours, WQ1200⁰C, 8hours, ACSampling region isrelatively small forthe large grains.Further analysiswith largersampling regionwill be done toaccurate measurethe grain size.18NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Outlines1. Objectives2. As-built samples produced by L-PBF AM Characteristics of microstructures Confirmation of precipitates Effect of support on hardness value3. Post-build heat treatment Homogenization Aging4. Effect of heat treatment on microstructure5. Effect of heat treatment on surface oxidation6. Results and future works19NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Porosities in the middle of the samples after heat treatmentAs-built sample1200⁰C, 2hours, WQ1200⁰C, 8hours, WQ Question: Why there are severe porosities formed after high temperature heattreatment? Recalling the shielding gas used for heating and holding steps: Ar (0.97 liter per min) Procedure: Exam surfaces using optical microscopy and SEM20NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Preparation of the samplesThermocouple* Originalsurface onwhich SEMimageswere takenSurface appearanceafter heat treatment21NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsSample cuttingThermocouple hole* New surface for observingsurface oxidization* Center of this new surface notexposed to shielding gasCross section of sampleCIMJSEA
Confirmation of the oxidation layerOutside(exposed surfaceduring heat treating)Casting (1093⁰C, 2hrs, AC 982⁰C, 1hr, AC)22NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplications Cracking and porosity featuresobserved in all the exteriorsurfaces exposed to shielding gas Such features not observed in theunexposed interior Therefore, it is determined to beoxidation formed during hightemperature heat treatmentCIMJSEA
Comparison with literature dataThis studyLiterature1200⁰C, 8hours, WQ1200⁰C, 2hours, FAC*Cr2O3**γ (Ni-Cr-Fe) matrixSLM AM1. External oxidation scale2. Internal oxidation zone: thread like oxidesWrought1. Intergranular oxides penetrations* Qingbo Jia et al. “Selective laser melting additive manufactured Inconel 718 superalloy parts: high-temperature oxidation property and its mechanisms”,NSFI/UCRCCenterOptics & Laser Technology, 2014,pp.161-171for Integrative** V. Gatat et al. “High temperatureintergranular oxidation of alloy 718”, Superlloys 718, 625 and Derivatives 2005, TMS, 2005, pp. 559-569Materials Joining Further analysis ongoing to understand the severity of oxidation with improvedhigher flow rate of Ar)Science for (e.g.,Energy23 shielding conditionApplicationsCIMJSEA
Outlines1. Objectives2. As-built samples produced by L-PBF AM Characteristics of microstructures Confirmation of precipitates Effect of support on hardness value3. Post-build heat treatment Homogenization Aging4. Effect of heat treatment on microstructure5. Effect of heat treatment on surface oxidation6. Results and future works24NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Summary and conclusions1. Characterization of as-built microstructures: Fine dendrites with continuous network of the Laves phase NbC and delta, two other common precipitates, were not observed2. Post-built heat treatment: Laves phase dissolved more at higher temperature and longer hold time. There was still a smallamount of Laves remaining after homogenization at 1200⁰C for 8 hours. Significant grain growth took place. Delta phase appeared in casting condition (1093⁰C 2hrs AC 982⁰C 1hr AC), which could have adetrimental effect on the mechanical properties. Oxidation layers occurred on the exposed surfaces.3. Microstructure after aging Hardness comparable to wrought condition Formation of strengthening precipitates (γ’’ and γ’)Plans for future work1. Characterization for heat treatment samples Homogenization to completely dissolve the Laves phase2. Creep test for aging conditions of INCONEL 71825NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Thank you26NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Effect of heat treatment on microstructures Homogenization: Decreased hardness value (30%) for the higher peak temperature (1100⁰C and 1200⁰C) Decreased hardness value (20%) for casting condition (1093⁰C 2hrs AC 982⁰C 1hr AC) Increased grain size ( 200%) for the higher peak temperature (1100⁰C and 1200⁰C) Control factors of hardness value: holding time and peak temperature Homogenization aging (without solution annealing): Formation of strengthening precipitates (γ’ and γ’’) even though Laves phase was notcompletely eliminated in the homogenization step27NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Oxidation process at high temperature atmosphereFurnace chamberOxygen molecules (O2)Sample (free electrons: 𝒆𝒆 )Furnace chamber Oxygen molecules can collide with thesample surface, breaking into oxygen atomsFurnace chamberOxygen atoms (O)Oxygen atoms (O)Oxidation layerSample (free electrons: 𝒆𝒆 ) Chemical absorption by interaction betweenthe free electrons of the base alloy and theoxygen atoms The nucleated oxides grow perpendicular tothe surface of the base alloy Pores can act as the crack initiatorsdue to stress concentrationsNSF I/UCRC Centerfor IntegrativeQingbo Jia et al. “Selective laser meltingMaterialsadditiveJoining manufactured Inconel 718 superalloy parts: high-temperature oxidation property and its mechanisms”,for EnergyOptics & Laser Technology, 2014,Sciencepp. 161-171ApplicationsCIMJSEA28
Peak temperature and timeRemaining Laves phase fraction as function of homogenization temperature and time 𝟐𝟐. 𝟒𝟒𝟒𝟒 𝟏𝟏𝟏𝟏 𝟏𝟏𝟏𝟏 𝒕𝒕𝐞𝐞𝐞𝐞𝐞𝐞( 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎 𝑻𝑻)𝑹𝑹 𝐞𝐞𝐞𝐞𝐞𝐞Time Temp.(hour)(⁰C)RemainingLaves phasefraction (%)Time(hour) 𝟏𝟏𝟏𝟏𝟏𝟏RemainingTemp.Time Temp.Laves phase(hour)(⁰C)(⁰C)fraction (%)RemainingLaves phasefraction 00601140*0NSF I/UCRC CenterCIMJSEAfor Integrative* MIAO Zhu-jun et al., “Quantitativeanalysis of homogenization treatment of INCONEL718 superalloy”, Trans. Nonferrous Met. Soc. China, 2011,Materials Joining291009-1017Science for EnergyApplications
Comparison of hardness maps for homogenized samplesThe same scale: 200 290 HVN1100⁰C, 2hrs, AC1100⁰C, 2hrs, 11093⁰C, 2hrs and 953⁰C 1hr, AC30NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEAAvg.251Max.292Min.200
Comparison of hardness maps for homogenized samplesThe same scale: 200 290 HVN1100⁰C, 2hrs, AC1100⁰C, 2hrs, Forced-ACAvg.248Avg.2621100⁰C, 8hrs, 731NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
Comparison of hardness maps for homogenized samplesThe same scale: 210 360 HVN1100⁰C, 2hrs, WQ321100⁰C, 8hrs, WQAvg.327Avg.235Max.359Max.265Min.300Min.217NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
8-AC33NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for 2-8-WQ
8-AC34NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for 2-8-WQ
As-BCasting 1100-8-WQ1200-8-AC1200-8-WQ The grain growth as the higher homogenization temperature Increased grain diameter ( 50%) on water quenched condition for the same peak temp.35NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
As-BCasting1100-8-WQ1200-8-AC1200-8-WQ The reduced hardness values show the higher misorientation angles However, little difference in the misorientation angles all peak temperatures36NSF I/UCRC Centerfor IntegrativeMaterials JoiningScience for EnergyApplicationsCIMJSEA
8-ACB2-2-S-12-8-ACB2-8-N-LF-12-8-WQ Difficult to decidetheeffect of high amount of misorientation anglesNSF I/UCRCCenterfor IntegrativeMaterials Joining due to small number of grains in heat treated conditions37Science for EnergyApplicationsCIMJSEA
Schematic of non-uniform precipitationNb rich PPT.Nb diffusionalong G.BPPT. alongprior G.B.NbNb depleted areaAs-received conditionNSF I/UCRC CenterVery slowlattice diffusionAt temp.,prior to deformationCIMJSEANewly recrystallized grains(Nb depleted area)Aging response,after deformationPaul J. Diconza, “Homogenization forandIntegrativethermomechanical processing of cast alloy 718”, The Minerals , Metals & Materials Society, 1991, pp. 161-7138Materials JoiningScience for EnergyApplications
1. Homogenization: Holding at 1093⁰C for 2hours and air cooling 2. Aging: Holding at 718⁰C for 8 hours and then furnace cooling 621⁰C for 10 hours (including cooling time from 718⁰C to 621⁰C) 3. Shielding gas for heating and holding steps: Ar (0.97 liter per min) 718 ⁰C 621 ⁰C 8 hours. 10 hours Furnace cooling Cooling in Ar
To observe the heat treatment process for a 4340 and a 1018 (A36) steel sample and effect on properties. To observe the heat treatment process for a 2024 aluminum sample and effect on properties. To observe the effect of heat treatment on 260 Brass sample and effect on properties. Relate microstructure to mechanical properties
responsiveness to heat treatment. The furnace is the most important equipment used in the heat treatment process. Heat treatment furnace with effective temperature sensing, heat retaining capacity and controlled environment are necessary for heat treatment operations to be successfully performed (Alaname and Olaruwaju, 2010). Some of the
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After investigating the impact toughness of the heat-affected zone for Grade 91 steel welds, it was discovered that 760 C for 2 h postweld heat treatment can significantly increase the cross-weld toughness of the heat-affected zone BY B. SILWAL, L. LI, A. DECEUSTER, AND B. GRIFFITHS KEYWORDS Heat-Affected Zone (HAZ) Grade 91 Postweld Heat .
heat, a heat pump can supply heat to a house even on cold winter days. In fact, air at -18 C contains about 85 percent of the heat it contained at 21 C. An air-source heat pump absorbs heat from the outdoor air in winter and rejects heat into outdoor air in summer. It is the most common type of heat pump found in Canadian homes at this time.
HEAT CHANGE OVER VALVE B C R L2 L1 (HOT) Typical 3H/2C or 2H/1C Heat Pump System System: Indicates current mode of operation. AUXILIARY HEAT RELAY EMERGENCY HEAT RELAY Terminal 2 Heat 2 Cool Conventional System 2 Heat 2 Cool Heat Pump System 3 Heat 2 Cool Heat Pump System RC RH C B O G W/E W2 Transformer power (cooling) Transformer power .
Plants were then exposed to a heat shock treatment and sampled. As controls, we used well-watered plants (control), drought-stressed plants that were not subjected to heat shock (drought), and well-watered plants that were subjected to heat shock (heat shock). All plants were analyzed and sampled at the same time (after the heat shock treatment).
and brazing. Successful post-sintering heat treatment of PM parts involves the proper selection of material, heat treating parameters and heat processing equipment. There are many factors that influence the heat treatment of PM parts and that ultimately determine the prope
