The formation of precipitates during thermal processing of microalloyed steels greatly influences their mechanical properties. Precipitation behavior varies with steel composition and temperature history and can lead to beneficial grain refinement or detrimental transverse surface cracks. This work presents an efficient computational model of equilibrium precipitation of oxides, sulfides, nitrides, and carbides in steels, based on satisfying solubility limits including Wagner interaction between elements, mutual solubility between precipitates, and mass conservation of alloying elements. The model predicts the compositions and amounts of stable precipitates for multicomponent microalloyed steels in liquid, ferrite, and austenite phases at any temperature. The model is first validated by comparing with analytical solutions of simple cases, predictions using the commercial package JMat-PRO, and previous experimental observations. Then it is applied to track the evolution of precipitate amounts during continuous casting of two commercial steels (1004 LCAK and 1006Nb HSLA) at two different casting speeds. This model is easy to modify to incorporate other precipitates, or new thermodynamic data, and is a useful tool for equilibrium precipitation analysis.

An adhesive bonding process is presented that utilizes sub-micrometer thick bondlines of all-aromatic thermosetting copolyesters (ATSP) for the assembly of polyimide membranes in silicon-based sensors and actuators. Due to the unique ability of ATSP to form void-free self-adhesive bonds through solid-state interchain transesterification reactions, sub-micrometer adhesive bonding technology offers new avenues for the precision assembly of high-performance, three-dimensional microscopic and mesoscopic devices. As a model process, PMDA-ODA polyimide membranes, 4-6 µm thick, are fabricated on glass carrier substrates, selectively bonded, transferred, and assembled on bulk-micromachined silicon substrates in the fabrication of mesoscopic circular diaphragm structures, 2-8 mm in diameter. Experimental load-deflection behavior of adhesively bonded polyimide diaphragms demonstrate that assembled membranes exhibit a tensile residual stress of 19 MPa, a value roughly equal to that measured for a PMDA-ODA polyimide film (derived from a thermally imidized polyamic acid precursor) deposited directly on silicon. Using a standard blister-type peel test, the debond energy range of an assembled polyimide membrane is shown to be 15-23 J m −2 , approximately 15-25% of the debond energy measured for a PMDA-ODA polyimide film deposited directly on a silicon substrate with a native oxide surface.

A new family of polymer, namely hyperbranched thermosetting poly(imide−ester) (HBPIE), was successfully prepared by the esterification reaction between a hyperbranched oligoimide terminated with carboxylic end groups (−COOH) and a hyperbranched oligoester terminated with acetoxy end groups (−OAc). The hyperbranched oligoimide has a degree of branching of one, M w = 14 180, and polydispersity Pd = 1.953. The −OAc-terminated oligoester has M w = 7000 and polydispersity Pd = 1.17. The NMP solution of the oligoimide and oligoester had excellent film-forming properties. HBPIE films cured from these two oligomers are thermally stable and display surface area of 83 m2/g due to their intrinsic microporosity (pore size 12.7 Å). The submicrometer thin film of HBPIE also displays an intermediate dielectric constant and high dielectric breakdown strength.

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ABSTRACT:The adhesion mechanism between polyimides and aromatic thermosetting copolyester (ATSP) involved in the solid-state bonding technique using submicrometer ATSP coatings was evaluated. The adhesion strength at the interface between ATSP and polyimide is strongly related to the diffusion of ATSP into the polyimide base layer. We used dynamic secondary ion mass spectrometry to study the interface width between deuterated ATSP and polyimides and found that the interface between ATSP and poly(4,4Ј-diphenylether pyromellitimide) (PMDA-ODA) is wider than the interface between ATSP and poly(pphenylene biphenyltetracarboximide) (BPDA-PPD) because of the less rigid chain in the PMDA-ODA. By partially curing both polyimides, the interface width was greatly increased, which could lead to an improved adhesion at the interface between polyimide BPDA-PPD and ATSP. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: [3843][3844][3845][3846][3847][3848][3849][3850][3851][3852][3853][3854][3855][3856] 2004