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September 14, 2011 Application of Electro-Spark Deposition for the Joining of Dissimilar Metals Jerry E. Gould Technology Leader, Resistance and Solid-State.

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Presentation on theme: "September 14, 2011 Application of Electro-Spark Deposition for the Joining of Dissimilar Metals Jerry E. Gould Technology Leader, Resistance and Solid-State."— Presentation transcript:

1 September 14, 2011 Application of Electro-Spark Deposition for the Joining of Dissimilar Metals Jerry E. Gould Technology Leader, Resistance and Solid-State Welding Phone:

2 Topics to be Addressed  Functionality of the electro-spark deposition process  Application for joints between Ni-based superalloys and refractory metals  Observed microstructures  Resulting mechanical properties  Interpretation of effective cooling rates  Implications for dissimilar joint metallurgy

3 Electro-Spark Deposition (ESD) Process  ESD processing characteristics ─Repeat fire capacitive discharge power supply ─Discharge pulse widths on the order of 35 μs ─Peak currents on the order of 100s of amps  ESD torch ─Hand held ─Rotating electrode  Short circuit sparking  Transfer of small metal volumes (microns in diameter) to substrate

4 Firing Efficiency of Electro-Spark Deposition  Firing rates defined by control system  Individual pulse widths on the order of 10s of micro- seconds  Variable contact pressures affect workpiece resistance and current flow  Sparking “efficiency” quality tool for assessing deposition characteristics  % sparking efficiency deemed ideal

5 Electro-Spark Deposition (ESD) Process  ESD deposit characteristics ─Deposit layers typically microns thick ─Deposition rates typically <100 μg/s ─Multiple layers to create a deposit ─Virtually no heating of the substrate  Application to complex materials joining problems ─Small splat sizes to achieve a fine material grain structure ─Fast cooling rates (> o C/s) ─Non equilibrium solidification and suppression of solid-state transformations

6 Thermal Analysis of Various Localized Deposition Processes Arc and Laser Processes: ESD: Arc and Laser Processes: ESD:

7 Ni-Superalloy to Refractory Metal Joints for Space Nuclear Propulsion  Nuclear-powered space propulsion  Lunar-based power  Gas cooled reactor  Brayton cycle energy conversion  Refractory metals at/near the reactor  Nickel-based superalloys at/near the turbine  Need for dissimilar materials transitions

8 Material Combinations of Interest  Refractory to nickel-based superalloy joints  Refractory metal alloys ─Mo-47.5 Re ─T-111 (Ta-8%W-2%Hf)  Nickel-based superalloys ─Hastelloy X ─Mar M247  Melting point suppression associated with eutectics ─Solidification cracking ─Liquation cracking  Intermetallic formation ─Joint ductility ─Pre-mature fracture

9 Electro-Spark Deposition Welding Trials  ASAP 50-μF electro-spark deposition system  Welding trials to be done in chamber ─Hard glove box ─Oxygen levels <1 ppm  Material combinations ─Mo-47Re strip to Mar M247 strip ─T-111 strip to Mar M247 strip ─Mo-47Re strip to Hastelloy X strip ─T-111 strip to Hastelloy X strip  All materials 0.5-mm flat stock Hard Glove Box with ESD Unit used Throughout these Trials ESD Torch and Manual Manipulation used Throughout these Trials

10 Electro-Spark Deposition Welding Trials – Set-Up  Bonding procedure ─Machined joint prep ─ESD fill ─Joint prep on reverse side ─Final fill  Practice taken from EWI experience  Small adaptations made to maintain surface quality ESD Electrode Weld groove to be filled with deposited metal ESD Specimen

11 Electro-Spark Deposition Welding Trials  Welding of ½ tensile specimens  Weld prep  Deposition practice: ─Hastelloy X electrode (1.5-mm diameter) ─40-μF capacitance ─120-V charging voltage ─500-Hz firing rate  Three specimens for materials combination ─One for metallographic sections ─Fill patterns ─Internal fill quality ─Intermetallic formation ─Two samples each for mechanical testing Joint Preparation and Electrode Orientation for the ESD Welds made in this Study ESD Weld Current Waveform Taken from a Representative Deposit

12 Wrought Base Metal Microstructures Microstructure of the Mo-47%Re Base Metal Typical of the Material used in this Study Microstructure of the Hastelloy X Base Metal Typical of the Material used in this Study

13 MarM 247 Base Metal Microstructures Coarse-Grained MarM 247 Base Metal Fine-Grained MarM 247 Base Metal

14 Electro-Spark Deposition Welding – Mo-47%Re to Hastelloy X  Procedure included ─Fill of initial groove ─Formation of back groove ─Filling back groove ─Sideplates used to improve joint geometry  Fill nominally >99% dense  Splat size nominally 10-μm thick  Fill showed good adhesion to both components  Processing time: 8 hr/specimen Final Geometry of a ESD Joint Cross Section of a Mo-47%Re to Hastelloy X ESD Weld Microstructural Details of the Hastelloy X Deposit

15 Electro-Spark Deposition Welding – Mo-47%Re to Hastelloy X  Hastelloy X/deposit interface ─Good adhesion of deposited material ─No degradation of base material noted ─Splat size in deposit on the order of the BM grain size  Mo-47%Re/deposit interface ─Good deposit adhesion noted ─Little or no dillution with base metal ─No evidence of second phases Details of the Hastelloy X/Deposit Interface Details of the Mo-47%Re/Deposit Interface

16 Electro-Spark Deposition Welding – Mo-47%Re to MarM 247  Joint macrostructure ─Fill characteristics similar to that for other ESD welds ─Apparent adherence to both the Mo-47%Re and MarM 247 materials ─Two-side deposition evident  MarM 247/deposit interface ─Good adhesion of deposited material ─Apparent reaction zone between the base metal and deposited splats ─Interface morphology similar to that seen for magnetic pulse welds ─Reaction zone on the order of microns thick Cross Section of a Mo-47%Re to MarM 247 ESD Weld Details of the MarM/Deposit Interface

17 Electro-Spark Deposition Welding – T-111 to Hastelloy X  Joint macrostructure ─Fill characteristics similar to that for other ESD welds ─Apparent adherence to both the T-111and Hastelloy X materials ─Two-side deposition again evident  T-111/deposit interface ─Good adhesion of deposited material ─No apparent reaction zone ─No apparent thermal degradation of the base material Cross Section of a T-111 to Hastelloy X 247 ESD Weld Details of the T-111/Deposit Interface

18 Electro-Spark Deposition Welding – T-111 to MarM 247  Joint macrostructure ─Fill characteristics similar to that for other ESD welds ─Apparent adherence to both the T-111and MarM 247 materials ─Two-side deposition again evident Cross Section of a T-111 to MarM 247 ESD Weld

19 Tensile Properties of ESD Welded Ni-Base Superalloy/ Refractory Metal Combinations  Duplicate tensile tests conducted for each material combination  Tensile yield strengths at or above that of the Hastelloy X filler  Elongations dependent on: ─Strengths of the substrates relative to the filler ─Ductility of the individual substrates MaterialYS (MPa)UTS (MPa) MarM Mo-47%Re T Hastelloy X Base Metal Properties of the Various Substrates Taken from Standard Reference Texts Duplicate Tensile Test Results from Each Material Combination ESD Welded with a Hastelloy X Filler Refractory MetalSuperalloyYield stress (MPa)UTS (MPa)% strain Mo-47ReMarM Mo-47ReMarM Mo-47ReHastelloy-X Mo-47ReHastelloy-X T-111MarM T-111MarM T-111Hastelloy-X T-111Hastelloy-X

20 Estimation of Cooling Rates During Electro-Spark Deposition – Stage 1: Heat of Fusion Driven  Two stage analysis ─Heat of fusion conduction ─Latent heat conduction  One dimensional non- steady-state solution (1)  Conduction driven boundary condition (2)  Heat generation through solidification (2)  Defined thermal gradient at solidification boundary (3)  Integration to define solidification time (4)  Defined transition time between solidification and latent heat driven cooling rates (5) (1) (2) (3) (4) (5)

21 Estimation of Cooling Rates During Electro-Spark Deposition – Stage 2: Latent Heat Affects  Transition to latent heat driven conduction  Definition of thermal gradient from solidification analysis (6)  Substitution to define final expression (7)  Predictions of cooling rates at solidification terminus  Cooling rates from 10 7 to o C/s  Cooling rates affected by conductivity of the substrate (6) (7)

22 Metallurgical Implications of ESD welding Dissimilar Material Joints  Effects of high cooling rates on solidification ─Equally high solidification rates ─Dendritic solidification without segregation ─Solidification morphology surface tension rather than compositionally driven ─Elimination of drivers for solidification cracking ─Potential for a wide range of solid- solution phases  Effects on solid-state phase transformations ─High cooling rates suppress second phases ─Allows super-saturated phases to exist at room temperature ─Potential for complex phase distributions with post-weld heating  Parallels in other pulse weld technologies ─Magnetic pulse welding ─Percussion welding Hastelloy X Deposit on a Mo-47%Re Substrate

23 Summary  Characteristics of electro-spark deposition processing ─Repetitive capacitive discharge process ─Deposition volumes on the order of 100 μm 2 ─Adaptable to difficult materials combinations  Electro-spark deposition welding Ni-based superalloys to refractory metals ─Adaptable to all material combinations ─Fill densities >98% ─No evidence of detrimental phase formation ─Processing times ~8 hr/sample ─Mechanical properties defined by those of the base materials  Thermal analysis of the ESD process ─One dimensional analysis ─Based on solidification of a single splat ─Cooling rates at termination of solidification on the order of 10 7 to o C/s  Influence of high cooling rates ─Solidification without apparent segregation ─Suppression of solid-state phase transformation products ─Presence of uniform non-equilibrium super saturated phases  Considerable potential for dissimilar material combinations

24 Questions? Jerry E. Gould Technology Leader, Resistance and Solid-State Welding Phone:

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