High temperature Ni-based super alloy casting process advancement

Final Report Summary - HITECAST (High temperature Ni-based super alloy casting process advancement)

Executive Summary:
The aim of the HITECAST project was to establish castability and weldability limits of Alloy B which is an enabler material for manufacturing a lightweight turbine components with higher work temperature in comparison with the currently fabricated based on IN718 alloy. The 24-months project is structured in 5 technical work packages and one addressing management and coordination. The consortium consists of jet engines manufacturer (WSKRZ) and two technical universities (WUT and RUT).
The main objectives of the HITECAST project were:
• Designing 3D geometrical models of samples, runners elements, dies and turbine component for computational simulation and for performing wax assembles elements dies for wax injection technique.
• Preparation of thermal properties data base for materials used in the numerical modeling of casting process (Alloy B, shell moulds and shell raping insulator material)
• Castability numerical modeling via ProCast software as function of: alloy capacity, alloy chemical composition, melting, casting and shell temperature, geometry of runners system, thickness of cast section, pouring profile, shell mould material, number of shell coats, filtering system
• Numerical modeling of EX structure in cast made in AlloyB
• Optimization of wax patterns and wax assembles geometry for demo parts castings
• Optimization of shell mould systems for investment process of manufacturing turbine demo parts castings
• Optimization of investment casting parameters for Alloy B in context of manufacturing demo parts castings
• Establishment and improvement of castability for Alloy B – defining critical wall thickness of casts
• Optimization of heat treatment conditions for as cast Alloy B
• Casting of ten demo parts per drawing with required quality
• High temperature characteristics of AlloyB by Gleeble metallurgical simulator
• Optimization of welding parameters like: preparation method, type of welding torch, type of torch nozzle, type of shielding method, welding current and filler material in context of repairing welding of turbine demo parts castings
• Casting of ten demo parts per drawing with required quality
In view of the obtained results can be concluded that Alloy B is a good candidate for casting and welding of large and thin-walled elements of aero engine components. All objectives, deliverables and milestones predicted in the Annex 1 of GA nr 296250 during HITECAST project duration have been fulfilled.

Project Context and Objectives:
Present report concerns detailed description of obtained deliverables and milestones in context of:
1. Development of numerical simulator of casting process (based on the ProCast® software) to support the experimental activities and interpretation of the experimental results.
2. Experimental studies of castability limit parameters of Alloy B.
3. Development of the casting process and challenging the minimum wall thickness below 2 mm.
4. Studies of macro, microstructure and mechanical properties of as cast Alloy B.
5. Optimizing of the welding process parameters of the cast parts made from Alloy B.
6. Demonstration of the capacity efficienty of the developed technology for casting turbine exhaust demo parts.
For major objectives achiving at first (WP1) based on technical documentation (drawings) supplied by GKN Sweden (Topic Manager Institution), 3D computational models of demo parts was designed as well as simple shape geometry samples for castability and weldability trails and samples to carry out an investigation of microstructure and mechanical properties of castings. Parallel to designing wax assembles for each samples geometry and demo parts, 3D models of dies for wax injection technique were designed. Alloy B was characterized by DTA as a results whole temperatures of phase transformations during solidification were achieved. The results of Work Package 2 of HITECAST include numerical simulations of pouring and solidification for casting geometries designed in WP1.
• Wedge geometry – pouring, solidification and volumetric part of the solid phase in time; grain microstructure simulation with statistical investigation of an average grain area and their diameter.
• Archimedean spiral assembly – pouring and solidification characteristic versus time
• Comparison of numerical simulation results of pouring and solidification paths for AlloyB and IN 718 alloy.
• Demo parts – pouring, solidification and shrinkage porosity investigation in the volume of the component; two different gating system was tasken in consideration.
During realization of WP3 results achieved from WP1 and WP2 were validated and optimized by through casting trials in industrial EX and semi-industrial EX/DX furnaces. Feasible solutions of assembly geometry and investment casting process parameters obtained from WP2 (like: metal capacity, metal chemical composition, melting, casting and shell temperature, thickness of cast section, pouring profile, shell mould material, number of shell coats, filtering system) were validated. Ultimately, the most optimal solution was achieved. Task was executed in several steps, as follows. Wax assembles for samples were manufactured utilizing Rapid Prototyping Technique (RUT) and wax injection technique (WSKRZ).
Manufactured wax assembles were provided to WSKRZ and RUT investment foundry units for shell mould manufacturing and casting. Three different shells system were used during casting processes. Casting trials and samples investigations procedure were scheduled as follow:
1. Casting trials:
a) Fluidity tests for Alloy B and IN 718 alloys – Archimedean spiral geometry of pattern
b) Castability trials – “wedge” geometry of pattern” consisting of quality inspections of castings (visual, FPI and X-rays, chemical composition) made from Alloy B and IN 718 alloys; macrostructure investigations as cast state Alloy B and IN 718 alloys, microstructure investigations as cast state Alloy B, Hardness and microhardness tensile and stress rupture tests as cast state Alloy B.
c) Casting trials for mechanical tests samples .
Casting processes were done simultaneously using two furnaces (industrial EX-WSKRZ and semi-industrial EX/DXRUT). Use of two furnaces decreased the overall time needed to execute a designed number of casts with different melt pouring and shell firing temperatures. As a primary material for casting trials and investigations Alloy B was used. IN 718 superalloy was used during “fluidity and castability” casting trials as reference material. Casting trials for Alloy B were iterative (and supported by ProCast modeling – WP2 and differential thermal analysis (DTA) investigations) until proper cast samples with homogeneous macro and micro structure and required mechanical properties was fabricated. The quality of castings was inspected utilizing several techniques, such as: NDT (visual, FPI, X-rays inspections), macro-, microstructure and chemical composition studies (LM, SEM, TEM, XRF, EDS, WDS, AES, EELS) and mechanical tests: hardness, microhardness, tensile and stress rupture. Finally, authors obtain:
• Optimal solution for geometry of wax assemblies and shell moulds,
• Optimal solution for investment casting process parameters,
• Limits for the minimum wall thickness of castings with required properties,
• Full macro and microstructure characteristic of as cast Alloy B superalloy,
• Mechanical properties of as cast Alloy B for wide range of stress and temperature loading.
In the next step as cast Alloy B was heat treated. The multistage HT consisting of HIP/homogenization, solution annealing, solution treating and age hardening have been applied. Microstructure of heat treaded samples were detailed characterized by LM, SEM, TEM, XRF, EDS, WDS, EELS techniques. Mechanical behavior of HT AlloyB was investigated during tensile and stress rupture tests. Failure mechanism has been defined based on detailed fractography and microstructural studies (LM, SEM and TEM techniques were applied). Based on obtained results authors achieved:
• Optimal solution for HT process for Alloy B in cast state,
• Mechanical properties data base for cast and heat treated Alloy B for wide range of stress and temperature loading,
• Full microstructure characteristic of cast and heat treated Alloy B superalloy,
• Influence of heat treatment and mechanical test conditions on microstructure and failure mechanism of cast and heat treated Alloy B superalloy.
Weldability trials were supported by high temperature characteristics of Alloy B by Gleeble 3800 metallurgical simulator. Based on hot ductility tests several parameters has been determined for cast alloy B like: value of resistance force, nil strength temperature (NST), nil ductility temperature (NDT), NST- NDT range, ductility recovery temperature (DRT), strength recovery temperature (SRT), brittleness temperature range BTR and ductility recovery rate DRR. The hot ductility test results provided insight into material susceptibility to weld cracking such as heat affected zone liquation cracking. Based on obtained data in next step TIG method repairing welding parameters like: preparation method, type of welding torch, type of torch nozzle, type of shielding method, welding current and filler material were set up. Various geometries from simple shape samples (wedges) to HUB part geometry were used. Welded alloy was used in various conditions, such as cast, as solution heat treated and fully hardened.
Last stage of project was to perform final casting of ten demo parts per drawing with required technological quality. According to results received from WP1, WP2 and WP3, wax assembles (through Rapid Prototyping technique) and shell moulds were manufactured for demo part were manufactured. Based on results of WP3 included optimal solution of casting parameters (melting, pouring and solidification) and limits for the minimum wall thickness of castings induction melting and Investment Casting (VIM IC) process was used for manufacturing of demo parts made of AlloyB and demo parts made of IN 718. Casting trials were supported by computational simulations with using Procast software. Standard quality control procedures, common in aircraft industry, were applied to assess the quality of castings: FPI, X-Ray inspection, macrostructure characterization dimensions control (“white light measurments) and chemical composition. Additionally microstructure of demo parts were characterized (in as cast state and heat treated) by LM and SEM observations. Based on the obtained results it can be concluded that casting process parameters for demo part were successfully validated as obtained part fulfilled technical requirements.

Project Results:
Present report concerns description of results and obtained deliverables and milestones in context of:
• Designing 3D geometrical models of samples, runners elements, dies and turbine exhaust component for computational simulation and for performing wax assembles elements - WP1,
• Investment casting process simulations utilizing ProCast software to direct the experimental casting trials and support interpretation of the experimental results for casting IN718 and Alloy B - WP2,
• Casting trials for validation and optimization of technological parameters for receiving proper castability and microstructure and mechanical properties for Alloy B cast samples - WP3,
• Welding trials form optimization welding fabrication and weld repair process on Alloy B - WP4,
• Validation and optimization of casting parameters for fabrication of demo parts approved by aeroengine company - WP5.

3. RESULTS DESCRIPTION
3.1. WP1 - Computational designing elements of wax assembles and dies [1]
The main goals and objectives of the WP1 were designing 3D models of:
• “Simple shape” samples, wedge like geometry with different wall thickness, for investigations: castability and weldability,
• Archimedean spiral assembly for fluidity tests
• Samples for chemical composition measurements and mechanical tests (tensile stress rupture and for tests in Gleeble simulator),
• Demo part gating systems elements for all wax assembles,
• Dies for wax injection technique.
Based on technical documentation (drawings) supplied by GKN Sweden, 3D computational models of demo part was designed. All geometrical requirements were taken into consideration. According to specific geometry of final product, was necessary to design dedicated, thin-walled wedge like geometry samples, for castability and weldability trails and samples to carry out an investigation of microstructure and mechanical properties of castings. Parallel to designing wax assembles for each samples geometry and HUB, 3D models of dies for wax injection technique were designed. All 3D models were designed in ProCast® Software. Final stage of work was fabrication wax patterns and elements of gating systems by Rapid Prototyping technique for verification quality of wax assembles in context its utilization during realization of WP2-WP5.
Based on obtained results all deliverables and milestones predicted in the Annex 1 of GA nr 296250 for of WP1 (scheduled 01.02.2012 – 31.07.2012) have been fulfilled.
[1] Deliverable/Milestone Report of WP1: “Computational Designing Elements of Wax Assemblies and Dies” (HITECAST :JTI-CS-2011-01-SAGE-04-014), (Full report), VOLS:10166734-000-01, 2012, 40 p.

3.2. WP2 Casting process modeling via ProCast software [2]
The main goals and objectives of the WP2 were:
• O2.1. Preparation of thermal properties data base for materials used in the numerical modeling casting process (alloy, shell moulds and shell raping insulator material)
• O2.2. Castability numerical modeling via ProCast software as function of: metal capacity, metal chemical composition, melting, casting and shell temperature, geometry of runners system, thickness of cast section, pouring profile, shell mould material, number of shell coats, filtering system
• O2.3. Modeling of polycrystalline structure of castings
The results of Work Package 2 of HITECAST include numerical simulations of pouring and solidification process for elements designed in WP1:
• Wedge geometry – pouring, solidification and volumetric part of the solid phase in time; grain microstructure simulation with statistical investigation of an average grain area and their diameter,
• Archimedean spiral assembly – pouring and solidification in time
• Numerical simulation comparison of pouring and solidification for Alloy B and Inconel 718 alloys;
• Demo part– pouring, solidification and shrinkage porosity investigation in the volume of the component; two different gating system investigation,
Based on obtained results it can be concluded that all objectives and goals predicted in the Annex 1 of GA nr 296250 for WP2 (scheduled 01.02.2012 – 28.02.2013) have been fulfilled.

References:
[2] Deliverable/Milestone Report of WP2:
“Casting process modelling via ProCast software (Full Report)” (HITECAST :JTI-CS-2011-01-SAGE-04-014), VOLS: 10178499-000-01, 2013, p.69. – submitted and approved by Topic Manager Institution

3.3. WP3 - Casting trials – validation and optimization of results of ProCast simulations [3]
The main goals and objectives of the WP3 were:
• Optimization of wax patterns and wax assembles geometry
• Optimization of shell mould systems
• Optimization of investment casting parameters for Alloy B
• Establishment and improvement of castability for Alloy B – defining critical wall thickness of casts

The aim of this task was validation and optimization of the input from WP1 and WP2 through casting trials in industrial EX and semi-industrial EX/DX furnaces. During all casting trails only EX processes has been provide. Semi-industrial EX/SX furnace was equipped in “shell heater” with temperature controllers useful for changing and controlling shell mould temperature during pouring and solidification processes which is not allowed in standard EX industrial furnaces. Thermally controlled pouring and solidification was important for optimization of shell temperature, melting temperature and cooling rate for EX casting process of thin-walled parts manufactured from Alloy B alloy.
Feasible solutions of assembly geometry and investment casting process parameters obtained from WP2 (like: metal capacity, metal chemical composition, melting, casting and shell temperature, thickness of cast section, pouring profile, shell mould material, number of shell coats, filtering system) were validated. Ultimately, the most optimal solution was achieved. Task was executed in several steps, as follows. Wax assembles for samples were manufactured utilizing Rapid Prototyping Technique (RUT) and wax injection technique (WSKRZ). Several geometries of samples were manufactured as is shown in attached Figure 4.

Samples A and B are standard samples for investigations of chemical composition, and mechanical properties. Sample D is a typical for fluidity characterization of cast alloys. Geometry of sample D consist of bulk root and thin-walled airfoil (with thickness gradation) is dedicated for macro and microstructure investigations, controlling susceptibility to missruns formation and castability as well.
Manufactured wax assembles were provided to WSKRZ and RUT investment foundry units for shell mould manufacturing. At RUT castings trials one shell system (no. 1) were implemented, based on alumina and mullite fillers (developed by WUT). Shell primecoat consists of alumina flours and colloidal silica binder – Ludox AM. Alumina grit was applied as a primary stucco. Ten coats mould backup was manufactured by use of ceramic slurries based on mullite filler and colloidal silica binder - LudoxAM. Mullite grits were applied as back-up stuccos. Two different shell mould systems were used during WSKRZ casting trials. In shells from system no. 2 primecoat consists of zircon filler and colloidal silica binder. Alumina grit was applied as a primary stucco. In shells from system no. 3 primecoat was modified by adding 5%wt. of cobalt aluminate CoAl2O4 inoculant powder. Six coats mould backup was manufactured by use of ceramic slurries based on alumina silicates powders and colloidal silica binder in both cases. Following the shells were de-waxed, burned out, wrapped by insulating material and fired.
Casting trials and samples investigations procedure were scheduled as follow:
1. Differential thermal analysis (DTA) of Alloy B alloy.
2. Casting trials:
a) Fluidity tests for Alloy B and IN 718 alloys – Archimedean spiral geometry of pattern
b) Castability trials – “wedge” geometry of pattern”.
i. Quality inspections of castings (visual, FPI and X-rays, chemical composition) made from Alloy B and IN 718 alloys.
ii. Macrostructure investigations as cast state Alloy B and IN 718 alloys.
iii. Microstructure investigations as cast state Alloy B.
iv. Hardness and microhardness measurements as cast state Alloy B.
v. Tensile and stress rupture tests for as cast Alloy B.
c) Casting trials for mechanical tests samples.
d) Casting trials for Gleeble samples for Alloy B.
3. Heat treatment of cast Alloy B alloy
a) Microstructural characterization of cast and heat treated Alloy B alloy
b) Mechanical tests: tensile, stress rupture and hardness for cast and heat treated Alloy B alloy
c) Fractography and microstructural characterization of cast and heat treated Alloy B alloy after tensile and stress rupture tests.

Casting processes were done simultaneously using two furnaces (industrial EX-WSKRZ and semi-industrial EX/DXRUT). Use of two furnaces decreased the overall time needed to execute a designed number of casts. As a primary material for casting trials and investigations Alloy B was used. IN 718 superalloy was used during “fluidity and castability” casting trials as reference material. Casting trials for Alloy B were iterative (and supported by ProCast modeling – WP2 and differential thermal analysis (DTA) investigations) until proper cast samples with homogeneous macro and micro structure and required mechanical properties was fabricated.
The quality of castings was inspected utilizing several techniques, such as: NDT (visual, FPI, X-rays inspections), macro-, microstructure and chemical composition studies (LM, SEM, TEM, XRF, EDS, WDS, AES, EELS) and mechanical tests: hardness, microhardness, tensile and stress rupture. Finally, authors obtain:
• Optimal solution for geometry of wax assemblies and shell moulds,
• Optimal solution for investment casting process parameters,
• Limits for the minimum wall thickness of castings with required properties,
• Full macro and microstructure characteristic of as cast Alloy B superalloy,
• Mechanical properties of as cast Alloy B for wide range of stress and temperature loading.
In the next step as cast samples were heat treated. The multistage HT consisting of HIP/homogenization, solution annealing, solution treating and age hardening have been applied. Microstructure of heat treaded samples were detailed characterized by LM, SEM, TEM, XRF, EDS, WDS, EELS techniques. Mechanical behavior of HT superalloy was investigated during tensile and stress rupture tests. Failure mechanism has been defined based on detailed fractography and microstructural studies (LM, SEM and TEM techniques were applied). Based on obtained results authors achieved:
• Optimal solution for HT process for Alloy B in cast state,
• Mechanical properties data base for cast and heat treated Alloy B for wide range of stress and temperature loading,
• Full microstructure characteristic of cast and heat treated Alloy B superalloy,
• Influence of heat treatment and mechanical test conditions on microstructure and failure mechanism of cast and heat treated Alloy B superalloy.
Additionally, samples for weldability and Gleeble simulator tests (WP4) were cast and heat treated.
Based on obtained results it can be concluded that all objectives, deliverables and milestones predicted in the Annex 1 of GA nr 296250 for WP3 of HITECAST project have been fulfilled.

References:
[3] Deliverable/Milestone Report of WP3:
“Casting trials – validation and optimization of results of ProCast simulations (Full Report)” (HITECAST :JTI-CS-2011-01-SAGE-04-014), VOLS:10186123-000-01, p176. – submitted and approved by Topic Manager Institution

3.4. WP4 - Weldability tests [4]
The goal of WP4 is to perform welding test using simple test sample and final welding repair of cast demo parts with required technological quality.
Task was executed in several steps, as follows. Firstly high temperature characteristics of AlloyB was carried out using Gleeble 3800 metallurgical simulator. Based on hot ductility tests several parameters has been determined for cast AlloyB:
• Value of resistance force
• Nil strength temperature (NST)
• Nil ductility temperature (NDT)
• NST- NDT range
• Ductility recovery temperature (DRT)
• Strength recovery temperature (SRT)
• Brittleness temperature range BTR
• Ductility Recovery Rate DRR
The hot ductility test results provided insight into material susceptibility to weld cracking such as heat affected zone liquation cracking.
Based on obtained data in next step TIG method repairing welding parameters like: preparation method, type of welding torch, type of torch nozzle, type of shielding method, welding current and filler material were set up. Various geometries from simple shape samples (wedges – fig. 5) to demo part geometry were used. Welded alloy was used in various conditions, such as cast, as solution heat treated and fully hardened.

The quality of castings after TIG repairing tests were inspected utilizing several techniques, such as: NDT (FPI, X-rays inspection), microstructure characterization (LM and SEM) and mechanical properties (microhardness). Based on the obtained results can be concluded that welding process parameters for demo parts were successfully validated because obtained after repair samples and parts fulfilled technical requirements.
All objectives, deliverables and milestones predicted in the Annex 1 of GA nr 296250 for WP4 of HITECAST project have been fulfilled.

References:
[4] Deliverable/Milestone Report of WP4:
“Weldability tests (Full Final Report)” (HITECAST :JTI-CS-2011-01-SAGE-04-014), VOLS: 10178613-000-01, 2014, 29 p. – submitted and approved by Topic Manager Institution

3.5. WP5 - Final casting trials – summary [5]

The goal of WP5 was to perform final casting of ten demo parts per drawing with required technological quality.
According to results received from WP1, WP2 and WP3, wax assembles (through Rapid Prototyping technique) and shell moulds were manufactured. Based on results of WP3 included optimal solution of casting parameters (melting, pouring and solidification) and limits for the minimum wall thickness of castings induction melting and Investment Casting (VIM IC) process was used for manufacturing of 10 demo parts made of AlloyB and 2 demo parts made of IN 718. Casting trials were supported by computational simulations with using Procast software.

Standard quality control procedures, common in aircraft industry, were applied to assess the quality of castings: FPI, X-Ray inspection, macrostructure characterization dimensions control (“white light measurements”) and chemical composition. Additionally microstructure of demo parts were characterized (in as cast state and heat treated) by LM and SEM observations. Based on the obtained results it can be concluded that casting process parameters for demo part were successfully validated as obtained part fulfilled technical requirements.

All objectives, deliverables and milestones predicted in the Annex 1 of GA nr 296250 for WP5 of HITECAST project duration have been fulfilled.

References:
[5] Deliverable/Milestone Report of WP5:
“Final casting trials (Full Final Report)” (HITECAST :JTI-CS-2011-01-SAGE-04-014), VOLS: VOLS: 10178614-000-01, 2014, p. 109. – submitted and approved by Topic Manager Institution

Potential Impact:
Dissemination plan and exploitation of project results have been fully covered by Consortium Agreement, Implementation Agreement Non Disclosure Agreement signed by whole partners. The general results obtained by the partners within the project have been available by the partners and topic manager institution. However, specific data and technological solutions developed by a consortium are confidential due to competitiveness reasons.
The HITECAST project was focused on development (for new Alloy B) investment casting and repairing welding methods and its parameters to fabrication of lighter of turbine exhaust case components for new jet engines. Lightweight and efficient turbine components have great impact on reduction fuel consumption and emission of nitrous oxide by jet engines. It means major aim of this project is compatible with ACARE SRA 2020 objective - environmentally friendly aircraft engines. For GKN Areospace Engines Systems Sweden (aircraft company - Topic Manager Institution) responsible for “JTI-CS-2011-01-SAGE-04-014 topic call” global solution received in this project like:
• Vacuum induction melting and investment casting process for manufacturing thin–walled components made from Alloy B,
• TIG repairing welding of casts made Alloy B,
have significant business impact (increasing of competitiveness and cost reduction of manufacturing). It means that GKN Areospace Engines Systems Sweden will use the generated foreground in the development of future generation more environmentally friendly aircraft engines and achieved solutions are protected by non disclosure agreement.
Those results (listed below ) which are not protected by disclosure agreement will be disseminated in different courses of action.
• Numerical model for simulation of solidification process and macrostructure of Alloy B, Procast software with dedicated Alloy B data base.
• Multiscale methodology of microstructure characterization of AlloyB in as cast state and heat treated.
• Multiscale methodology of fracture analysis of AlloyB in as cast state and heat treated.
• Tensile and stress rupture behavior of cast AlloyB during mechanical tests under NADCAP certificate.
In detail, the industrial partner and universities have their own strategy to exploit or disseminate the results of the project. WSKRZ (industrial partner) disseminate the results within all of their business units of the company and transfer the knowledge and experiences gained to other technological applications especially for casting structural components. The universities (WUT and RUT) will present the knowledge at conferences (some results already present at NIMS Conference 2013) and through publications (major results already published see Table 5 and 6). Hitecast project increase also our competences and scientific reputation. Based on results of Hitecast project we established new international consortium and generate and submitted new R&D project entitled Failure analysis and damage mechanisms of newly developed, gamma-prime strengthened Ni - based superalloy (FAMEC SP1-JTI-CS-2013-02, 632468).

List of Websites:
All deliverables and milestones achieved during project realization posses status “confidentional”. Thus we do not present results in public domains without approval Topic Manager Institution . However was created e-room of Hitecast project. Team place was very useful for data storage and exchange in encrypted form. Access to e-room posses only consortium members and Topic manager Institution.

Final Report Summary - HITECAST (High temperature Ni-based super alloy casting process advancement)

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