Powder Materials Processing and Fundamental Understanding: Sintering
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Powder Materials Committee
Program Organizers: Elisa Torresani, San Diego State University; Kathy Lu, University of Alabama Birmingham; Eugene Olevsky, San Diego State University; Ma Qian, Royal Melbourne Institute of Technology; Diletta Giuntini, Eindhoven University of Technology; Paul Prichard, Kennametal Inc.; Wenwu Xu, San Diego State University
Tuesday 2:30 PM
March 21, 2023
Room: 25B
Location: SDCC
Session Chair: Elisa Torresani, San Diego State University; Diletta Giuntini, Eindhoven University of Technology
2:30 PM Invited
Sintering Mechanism for Polycrystalline Diamond: Randall German1; 1San Diego State University
Sintering concepts for mass transport and bonding of contacting grains are applied to the creation of polycrystalline diamond. In the presence of high pressure and high temperature, liquid cobalt facilitates solution-reprecipitation where interface surface defects limit the growth rate. The rate limiting kinetic step is the growth of dislocation spirals on the diamond surface. Calculations on the bonding rate, neck size, and level of strengthening are compatible with observed behavior. Improved sinter bonding is evident when excessive surface defects are introduced, leading to confirmation of pretreatments for the diamond particles in terms of increased surface sites and use of small (nanoscale) multiple modal mixtures of diamonds.
3:00 PM
Gravitation Effects on Sintering: Elisa Torresani1; Randall German1; Eugene Olevsky1; 1San Diego State University
With the increasing interest in space exploration and planet colonization, the research and advancement in producing components and repairing in space conditions through powder technologies have gained fundamental importance. Powder components in pressure-less sintering conditions ideally homogeneously shrink and retain their original shapes. However, sintering of real-world materials is influenced by many factors (e.g., temperature non-uniformity, friction forces, and gravity), which produce inhomogeneous densification and shape distortions in the final component. During sintering, non-uniform stress imposed by gravity influence the pore buoyancy, grain compression, and substrate friction, which affect the sintering densification, microstructure, properties, and dimensional uniformity. Ground-based and extraterrestrial sintering experiments on the liquid-phase sintering of tungsten heavy alloys are conducted, allowing to obtain densification and distortion data useful for extracting constitutive parameters needed to map the sintering response with and without gravity. It is shown that such models can enable predictions relevant to space-based repair and additive manufacturing.
3:20 PM
Minimizing Anisotropy and Cracking During Co-sintering of Layered Ceramics: Examples for Electronics, Energy and Catalysis: Diletta Giuntini1; 1Eindhoven University of Technology
The production of fully dense components made of multiple layered powders has been a long-standing challenge, and it is currently raising even more attention with the advent of additive manufacturing. Multi-layered ceramics and ceramic-metal composites are ubiquitous (capacitors, antennae, catalytic membranes, batteries…) and AM leads per se to layered components that in most cases need to undergo a sintering step. But their co-sintering is prone to be affected by anisotropy, distortions and even cracking, due to the different densification kinetics of each constituent. By modeling the sintering process in a simple finite-element-based platform, strategies to minimize these issues are defined. The stresses developed at the interfaces turn out to be key, and process optimization guidelines are drawn based both on the interface geometry and on the sintering routine.
3:40 PM
Analytical Models for Initial and Intermediate Stages of Sintering of Stainless Steel Manufactured by Binder Jetting: Alberto Cabo Rios1; Eugene Olevsky1; Eduard Hryha2; Mats Persson3; 1San Diego State University; 2Chalmers University; 3Digital Metal AB
The initial green porous structure created by the binder jetting printing is characterized by its high porosity (40–50%). Thus, initial and intermediate sintering stages progress within a large porosity range, where a complex combination of diffusion mechanisms drives the sintering behavior. In the continuum mechanics-based isotropic pressure-less sintering models, densification kinetics is driven by the balance between the effective sintering stress and bulk viscosity. In this study, different normalized bulk moduli expressions, inspired by Skorohod, Hsueh, and Abouaf sintering models, are used in the framework of the continuum theory of sintering. The material viscosity and bulk moduli are successfully obtained from dilatometry and grain size experiments. The bulk moduli proposed contain physical parameters, which depend on the interparticle stress distribution or/and the initial high reactivity of the BJ compacts. The results of modeling are compared with the experimental results on the sintering of binder jetted 316L stainless steel powder components.
4:00 PM
Multi-scale Modeling of the Electric Field Assisted Sintering Process: Larry Aagesen1; Stephanie Pitts1; Lucas Robinson2; R. Garcia2; 1Idaho National Laboratory; 2Purdue University
The electric field assisted sintering (EFAS) process involves tightly coupled physics that influence microstructural evolution in the particles being compacted. It is also an inherently multi-scale phenomenon, with the microstructure of the compact influencing the subsequent engineering-scale response of the sintering system. To improve understanding of how processing parameters influence microstructural evolution, we have developed a multi-scale modeling approach that couples a continuum-level model of the sintering system with a phase-field model for microstructural evolution of particles within the compact. The phase-field model couples the effect of chemical and electrical driving forces on microstructural evolution and includes the effect of charged defect segregation to surfaces and grain boundaries; this segregation leads to enhanced defect transport and heat generation at these interfaces in response to applied electric field. The effect of enhanced heat generation on particle neck growth and the influence of microstructural evolution on the engineering-scale model are demonstrated.
4:20 PM Break
4:40 PM Invited
Powder Metallurgy Co Base Superalloys and High Entropy Alloys: Beyond Ni-base Superalloys for High-temperature Applications: Jose Torralba1; Venkatesh Kumaran1; Alexander Mejia-Reinoso2; Alberto Meza3; Ahad Mohammadzadeh3; Dariusz Garbiec4; Monica Campos2; 1Universidad Carlos III Madrid-IMDEA Materials Institute; 2Universidad Carlos III Madrid; 3IMDEA Materials Institute; 4Poznan Institute of Technology
Ni-based superalloys have been the most popular material for high-temperature applications. The predominance of these alloys is related to their primary strengthening mechanism, the γ’ precipitation on an FCC γ matrix, together with the high solvus temperature of the γ’ precipitates. In recent years, alternative alloys, such as Co-based superalloys with a similar γ-γ’ microstructure and high-entropy alloys, have shown they can compete in the same field as Ni-based superalloys. In this competition, additive manufacturing and high densification powder metallurgy methods, have opened an opportunity window for PM. PM methods allow better chemical control, finer and homogeneous microstructure and, in AM methods, higher freedom in the design of the parts. The purpose of this work is to review some possibilities, including the use of Co, Co-Ni superalloys, and high-entropy alloys, as well as the use of PM methods (selective laser melting, field-assisted sintering), which provide competitive properties at high temperatures.
5:10 PM
Manufacturing of Porous Tungsten via Place-Holder Spark Plasma Sintering for Nuclear Fusion Applications: Trevor Marchhart1; Camila Lopez-Perez1; Martin Nieto-Perez1; Jean Paul Allain1; 1Pennsylvania State University
In a fusion reactor environment, plasma-facing components (PFCs) are exposed to extreme heat fluxes, large neutron loading, energetic particle bombardment, and high mechanical stresses. A potential PFC configuration in fusion reactors is porous tungsten with liquid lithium, which combines the benefits of high-Z and low-Z materials. 40-70% dense tungsten was manufactured via partial spark plasma sintering (SPS) of 800nm powders. Initial SEM images of the internal geometry show incomplete necking between particles. A high-temperature place-holder SPS (PHSPS) method is being developed which utilizes a secondary constituent particle that is present during sintering but removed afterwards in order to leave pores behind. PHSPS with tungsten introduces challenges due to tungsten’s high melting point and thus sintering temperature. However, this novel method is conjectured to produce much stronger porous tungsten, while providing much greater control over the pore structures. Work supported by DOE Contract DE-SC0021119.
5:30 PM
A New Hybrid Manufacturing Approach to Diffusion Bond and Functionally Grade Materials Demonstrated Through Titanium Alloys and Nickel-based Superalloys: Sam Lister1; Oliver Levano Blanch1; Martin Jackson1; 1University of Sheffield
Powder-based manufacturing processes such as Field Assisted Sintering Technology (FAST) have the potential to unlock a new era of multi-material or functionally-graded components for the aerospace industry. Currently, many are produced as monolithic single alloy structures and are over-engineered. As the drive towards net zero gathers pace, weight savings and subsequent emissions reductions due to more efficient component design are essential. This work demonstrates a method for engineering such components with site-specific properties via FAST, through diffusion bonding (FAST-DB) and functionally grading material (FGM). A number of titanium alloys and nickel-based superalloys have been successfully joined and functionally graded. Large-scale mechanical testing and extensive microstructural characterisation has been performed. Further assessments have been made of the bond’s response to downstream thermo-mechanical processing and machining operations. This technique offers designers a new dimension through which the next generation of high performance aerospace components may be produced.