Carbides Evolution in a Ni-16Mo-7Cr Base Superalloy during Long-Term Thermal Exposure
The effect of long-term thermal exposure on the carbide evolution in a Ni-16Mo-7Cr base superalloy was investigated. The results show that M12C carbides are mainly precipitated on the grain boundaries during thermal exposure, and the primary massive M6C carbides can be completely transformed to M12C carbides in situ at temperatures above 750 °C for long-term thermal exposure. The transformation from M6C carbides to M12C carbides is attributed to the release of C atoms from M6C, which results in the morphology changes of massive carbides, and stabilization of the sizes of M12C carbides precipitated on the grain boundaries.
Microstructural Evolution and Oxidation Behavior of Alloy Ni-13Mo-13Cr-9W-3Fe-3Ti-2Al During Isothermal Exposure at 900 °C
The microstructure evolution and oxidation behavior of alloy Ni-13Mo-13Cr-9W-3Fe-3Ti-2Al (alloy K4208), a newly developed Ni-Cr-W-Mo-based wear-resistant superalloy, were investigated by isothermal aging at 900 °C in air. Thermodynamic calculations, microstructure observations, electron probe microanalysis (EPMA), and precise microchemical analysis were used to study the microstructure evolution and oxidation mechanism of alloy K4208. The results showed that alloy K4208 was mainly composed of a P-like phase, M6C (and M12C) carbide, γ′ phase, μ phase, and γ matrix. During the 900 °C aging, the γ′ phase coarsened into irregular shapes, the M6C (and M12C) carbide decomposed, and the μ phase dissolved into the matrix, providing abundant Cr, Mo, and W for the growth of the P-like phase. Hence, the relationship between the different phases was established by element redistribution. In addition, the oxidation of alloy K4208 was a diffusion-controlled process, leading to the formation of a stable oxide layer composed of three parts: a thin layer of NiCr2O4 spinel located on the outermost side, a continuous Cr2O3 layer decorated with TiO2 in the middle, and an internal Al2O3 layer.
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.