When powder metallurgy structural parts are used in high-temperature environments, their creep characteristics are a core factor determining their service life and reliability. Creep, as the phenomenon of slow plastic deformation of materials over time under constant temperature and stress, is particularly pronounced in high-temperature environments. Due to the special manufacturing process of powder metallurgy structural parts, their microstructure contains a large number of pores, grain boundaries, and second-phase particles. These microscopic features are closely related to the high-temperature creep mechanism, making their creep behavior both follow the general laws of metallic materials and exhibit unique microstructural sensitivity.
The creep process of powder metallurgy structural parts is generally divided into three stages: the initial creep stage is dominated by dislocation slip, and the rate decreases due to work hardening after rapid deformation; the steady-state creep stage is controlled by diffusion, with atoms or vacancies migrating in the crystal lattice, and the deformation rate tends to stabilize; the accelerated creep stage is characterized by microcrack propagation and intensified grain boundary slip, ultimately leading to fracture. Compared with traditional forged or cast parts, powder metallurgy structural parts have a higher proportion of pores and grain boundaries, and these areas become weak points for stress concentration during creep. For example, high stress gradients at pore edges accelerate vacancy diffusion, promoting the nucleation and growth of creep cavities. Second-phase particles at grain boundaries may suppress creep by pinning dislocations or hindering grain boundary slip; the specific effect depends on the particle size, distribution, and interfacial bonding strength with the matrix.
At high temperatures, the creep mechanism of powder metallurgy structural parts is influenced by temperature, stress, and microstructure. Under low stress conditions, diffusion creep dominates, with atomic migration along grain boundaries or the lattice leading to viscous flow. Under high stress conditions, dislocation climb becomes the primary mechanism; dislocations overcome obstacles through thermal activation, forming subgrain boundaries or small-angle grain boundaries, which in turn induce grain boundary slip. Incompletely dense pores in powder metallurgy structural parts alter the local stress state, making creep deformation more concentrated around the pores and accelerating crack initiation. Furthermore, if component segregation or oxide inclusions exist during fabrication, these defects can act as nucleation sites for creep cavities, further reducing the material's creep resistance.
The creep resistance of powder metallurgy structural parts can be significantly improved by optimizing the manufacturing process. For example, post-processing techniques such as hot isostatic pressing (HIP) or hot forging can reduce porosity and increase density, thereby reducing stress concentration during creep. Adjusting the powder particle size distribution and pressing pressure can refine grain size, increase the number of grain boundaries, and utilize grain boundary strengthening mechanisms to suppress dislocation movement. Introducing dispersed strengthening phases (such as carbides, nitrides, or intermetallic compounds) into the alloy design can hinder dislocation climb and grain boundary sliding, extending the duration of the steady-state creep stage. For example, adding refractory elements such as tungsten and molybdenum to nickel-based superalloys can improve solid solution strengthening and simultaneously form a fine and stable γ' phase, significantly enhancing creep resistance.
The failure modes of powder metallurgy structural parts under high-temperature creep mainly include creep fracture and fatigue-creep interaction. Creep fracture typically manifests as intergranular fracture, with cracks forming and propagating at grain boundaries due to the connection of creep voids. However, under the combined effects of alternating stress and high temperature, fatigue cracks may preferentially initiate at pores or surface defects, subsequently interacting with creep damage and accelerating the fracture process. For example, in high-temperature, high-load components such as turbine disks in aero-engines, powder metallurgy structural parts must simultaneously meet the requirements of low-cycle fatigue life and high-temperature creep strength, posing a greater challenge to the co-design of creep-fatigue processes in materials. Research on the high-temperature creep characteristics of powder metallurgy structural parts requires a combination of experimental characterization and numerical simulation. High-temperature creep tests can obtain key parameters such as steady-state creep rate and creep limit, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can reveal the microstructural evolution after creep, such as dislocation substructure, grain boundary features, and second-phase morphology. Numerical simulations, by establishing crystal plasticity models or diffusion creep models, predict creep behavior under different microstructural states, providing theoretical guidance for process optimization. For example, by simulating the effect of different porosities on creep rate, the critical density requirement can be determined, guiding quality control in actual production.
The creep characteristics of powder metallurgy structural parts under high-temperature environments are the result of the combined effects of their microstructure and external conditions. By optimizing the manufacturing process, adjusting the alloy composition, and introducing reinforcing phases, their creep resistance can be significantly improved, meeting the stringent requirements of aerospace, energy, and other fields for high-temperature structural components. In the future, with the integration and application of new technologies such as materials genome technology and additive manufacturing, the design of creep performance for powder metallurgy structural parts will become more precise, further expanding their application boundaries in extreme environments.
