Crack Prevention in NiCr-Alloys when Processed by AM (L-PB) William Jarosinski March 8, 2017

Transcription

1 Crack Prevention in NiCr-Alloys when Processed by AM (L-PB) William Jarosinski March 8, 2017

2 Evolution into Metal Powders for AM Coating Service Since 1950s Metal Powders for AM A derivative of thermal spray powders Thermal Spray Powder Since 1960s (expanded in 1980s) Thermal Spray Equipment Since 1950s (expanded in 1990s) AM powder grows out of long history with thermal spray powders Page 2 3/10/2017

3 Cracks? Why do cracks form in Superalloys? function of chemistry function of process How do you reduce or eliminate cracks? change chemistry? change process? What can we learn from welding? how is chemistry changed? limitations and changes in the process? Cracks are generally not a good thing in Superalloys! Page 3 3/10/2017

4 Metal Polymer Types of AM Processes AM Processes Material Jetting Powder Bed Metal Process Detail Binder Jetting 3D printing PB Extruded Material Plastic, Extrusion ABS VAT Photopolymerization Sterolithography PB PF Powder Bed Fusion Direct Energy Deposition Selective Laser Sintering (SLS) Direct Metal Laser Sintering (DMLS) Laser Welding Laser Build-up Powder Fed PF Powder Bed & Powder Fed technologies use metal alloys Page 4 3/10/2017

5 NiCr Alloys by L-PB Process L-PB Parameters Alloy 625 & 718 are robust Interest and need for many other alloys Challenge is high productivity (thick) Larger melt pools can be more difficult Energy Density a power & volume DOE NiCr Matrix Alloy Ni-1287 (numbers) 40mm 40µm (0.040 mm) P o w e r Energy Density (J/mm 3 ) Speed Thickn 0.04 mm Hatching: 0.11 mm Parameters that set volume - thickness, hatch & speed Page 5 3/10/2017

6 Alloy 230 As-built: 40mm & 20mm Layers DOE Results 40mm Energy Density 20mm 67.5 J/mm J/mm J/mm J/mm J/mm J/mm 3 Originally, high energy density & thin layers had fewer & finer defects Page 6 3/10/2017

7 Fabrication of Crack-Free Alloy 230 by Direct Metal Laser Sintering Team Members: Jack Lopez, Katie Thomas, Phil Spagnolo, Ziyu Cai, Cory Richards Industry Sponsor: William Jarosinski Faculty Advisor: Dr. Xinghang Zhang Working with Purdue students and faculty to resolve issues Page 7 3/10/2017

8 Initial Conditions vs Bauer Conditions Parameters Initial Conditions Bauer Conditions Scan Speed (mm/s) Hatch Spacing (mm) Laser Power(W) Layer Thickness (μm) Energy Density (J/mm 3 ) to to Bauer conditions: 30mm layer, lower power & slower speed Page 8 3/10/2017

9 Solid vs. Hollow Samples Solid parts (30 mm) Scan Speed: 450 mm/s Energy Density: J/mm 3 Scan Speed: 600 mm/s Energy Density: J/mm 3 Scan Speed: 1050 mm/s Energy Density: 79.4 J/mm 3 Scan Speed: 1200 mm/s Energy Density: 69.4 J/mm 3 Thin wall parts (30 mm) Lower power & smaller volumes have fewer, if any, defects Page 9 3/10/2017

10 Moving from Parameters to Chemistry Parameters for Alloy 230 Layer thickness: 40 mm or greater (for productivity) Optimize parameters (hatch, speed & power) Chemistry for Alloy 230 Leverage welding chemistry modifications (230 vs. 230W, but...?) Optimize particle size distribution (PSD) Working to identify cause & prevention of cracks in difficult alloys Page 10 3/10/2017

11 Alloy 230 Chemistry Major Elements (weight percent) Minor Elements (weight percent) Ni balance Cr W Mo 1-3 Fe 3 * Co 5 * * maximum Mn ~ Si ~ Al ~ C 0.15 * La 0.05 * B * Others: Cu, N, O, P, S & Ti Filler material 230-W has lower minor elements, but what properties? Page 11 3/10/2017

12 AM Metal Powder Atomization Process 1 Batch Elemental vs. Ingot Melt (VIM) Pour Vacuum vs. blanket Tilt Pour 4 4 Atomize (metal stream droplets) Media (Gas - Ar vs. N2) 3 5 Close coupled 5 Collect Solidified particles 5 VIM atomization technology meets AM metal alloys needs Page 12 3/10/2017

13 Metal Powder Characteristics for AM Flow: good Size: -45/+15 mm (L-PB) Control: Melting (superheat, reactive elements) Morphology Solidification rate * Impurity Level: low Gas Content: low (function of PSD) Ti (e.g. O ppm) Fe (e.g. O ppm) Ni & Co (e.g. O ppm) Particle Voids and Satellites: low To be determined (specs) Gas atomized metal powders have the characteristics needed for AM Page 13 3/10/2017

14 Chemistry near Cracks Bulk Element Wt % C 3.9 O 0.80 Al 0.38 Mo 1.4 Cr 21.7 Fe 2.16 Ni 56.4 W 13.2 Near Crack Element Wt % C 16.5 O 1.6 Al 0.12 Mo 1.8 Cr 20.4 Fe 1.90 Ni 45.5 Carbide and boride phases form at the grain boundaries and limit grain growth and movement W 12.3 Phase identification by XRD being investigated at Purdue Page 14 3/10/2017

15 Microstructure Chemistry (material) + Process = Microstructure; which yields Properties Powder Properties L-PB Part Properties HT Goal: fix Processes, evaluate Properties and observe Microstructure Multiple processes to control in order to obtain repeatable properties Page 15 3/10/2017

16 Further Work Chemistry Tweak chemistry within spec to prevent cracks, but maintain properties Verify high productivity L-PB parameters are possible (properties?) As needed change chemistry to improve and take advantage of AM Chemistry for Alloy 230 Leverage welding chemistry modifications (230 vs. 230W, but...) Optimize particle size distribution (PSD) Crack prevention benefits from tighter chemistry control Page 16 3/10/2017

17 AM Lab Review Laser: Powder Bed Process Multiple EOS M 290 machines with 400 W lasers Powder Development TruForm 718 Evaluate particle size (PSD) Layer Thickness (20 & 40 vs. 60 mm) TruForm 625 SAE AMS AM specs (material, process, powder) Mechanical properties similar to cast Praxair AM Lab in Indianapolis, IN TruForm X Layer thickness (20 vs. 40 mm) Powder Reuse Study TruForm 230 Layer thickness (30 vs. 40 mm) Crack Prevention Study Superalloys are initial focus: Alloy 718, 625, HX & 230 Page 17 3/10/2017

18 Comments Process Smaller weld pools cool faster, generally less likely to have cracks Thicker layers are possible, but work is needed to verify robust process Slow cooling allows segregation and fixes grain boundaries Chemistry Tighten chemistry within spec to prevent cracks, but maintain properties Strategies are available to process difficult to weld alloys New compositions are possible, designed specifically for AM Improved controls can eliminate cracks in the microstructure Page 18 3/10/2017

19 TruForm Powders in Production Page 19 3/10/2017

20 Thank you For more information, please visit our website at praxairsurfacetechnologies.com/am Page 20 3/10/2017