No abstract

No abstract

No abstract

To accurately satisfy the size tolerance of metallic parts, it is necessary to take into account the dimensional change (DC ) caused by heat treatment, and the dispersion (DDC ) of the DC values. The information available on this topic for ADI is very scarce.The present work aims to determine DC and DDC on ADI and SAE 4140 steel parts and to analyze its influence on the size tolerances. Ductile iron and SAE 4140 steel specimens were used to compare DC and DDC caused by austempering, and quenching and tempering heat treatments. DC and DDC were also measured for several industrial parts of different ADI grades, having different chemical compositions, shapes and sizes.The results show that in average ADI suffer greater DC than SAE 4140 steel parts of similar mechanical properties, but, on the other hand, DDC is always lower for ADI than for steel.A more accurate prediction of the DC is then possible on ADI than on steels. This would allow the use of less strict machining tolerances, under better machinability conditions, when final operations can be done before heat treatment, producing series of ADI parts. This represents a technical and economical advantage for ADI in comparison with steel.The influence that the previous microstructure, the austempering temperature and the piece anisotropy, exert on the DC of ADI were also studied. The effects identified in this work are in agreement with previously reported results.KEY WORDS: dimensional change; dispersion of dimensional change; ADI and SAE 4140 steel; fabrication and machining tolerances; fabrication steps.

This work studies the influence of the PVD processing parameters on the characteristics of TiN and CrN coatings deposited on ADI substrates, austempered at 360°C, with different nodule counts and surface roughnesses. Coatings were applied by arc ion plating using an industrial reactor and different sets of parameters, with BIAS voltages, arc currents, chamber pressures and substrate temperatures varying from -100 to -250 V, 60 to 65 A, 0.7 to 2.8 Pa and 280 to 450°C, respectively. The effect of the different depositions conditions on the substrates microstructure was also analyzed. The existing phases, preferred orientation, surface topography, film thickness, hardness and adhesion of each coating were determined. The retained austenite content and hardness of each substrate were computed before and after coating deposition.The results obtained indicate that the different deposition conditions and coating materials evaluated do not generate significant changes neither in the resulting topography nor in the coating adhesion, which can be related to indices between HF1 and HF2. Coating adhesion was not affected by different substrate roughnesses. The combined reduction of BIAS voltage, arc current and chamber pressure leads to a decrease of TiN growth rate and hardness, while high substrate temperatures promotes an increase in TiN and CrN growth rates. Substrate temperatures around 300°C with deposition times of up to 240 min do not promote noticeable changes on the ausferritic microstructure, while temperatures of 400°C and above translate into a clear microstructural deterioration, even for short deposition times.

No abstract

The machining and heat treatment, employed in the fabrication of ADI parts, produce distortions and residual stresses that can increase the scrap rate. In the present study, dimensional changes, shape distortions and residual stresses due to machining and austempering were determined on internal gears of different chemical compositions, as-cast microstructures and machining-thermal cycle sequences. The influence of chemical composition and as-cast microstructure on dimensional change were found to be in accordance with the predictions obtained by Fuzzy modelling. Shape distortion resulted in an ovalization, whose magnitude depends upon the variation range of the residual stresses due to machining. Whereas residual stresses due to austempering were found to increase when the ovalization increases.The lack of information about the topics here studied, turn these results into a useful contribution to improve the fabrication quality of ADI internal gears. Besides, most of them can be applied to ADI parts in general.

The aim of this work is to study residual stresses (RS) in PVD TiN and CrN coated ADI substrates with different nodule counts, austempering temperatures and surface finishing methods (grinding and polishing). Coatings were applied by arc ion plating using an industrial reactor and different sets of processing parameters. Residual stress measurements were performed by x-ray diffraction using the sin 2 ψ method along two principal axes on the samples surface (parallel and perpendicular to the substrate abrasion direction). The film thickness, hardness and adhesion of each coated sample were also evaluated.The results obtained indicate that RS in TiN and CrN coated samples are compressive irrespective of the different substrates, surface finishing methods and processing parameters utilized. The parallel and perpendicular RS do not vary significantly, indicating a rotationally symmetric biaxial stress state. The RS of the coated samples are not influenced by the different substrate characteristics regarding microstructure, hardness and surface roughness. The microhardness and RS of TiN and CrN coated samples increase with film thickness. The increase in substrate temperature together with the decrease in the values of BIAS voltage, arc current and chamber pressure lead to microhardness and RS reduction. Grinding produces surface hardening and reduction of the compressive RS in the substrates, but causes no variations in the RS of the TiN and CrN coated samples. The adhesion strength quality of TiN and CrN coatings to ADI substrates can be related to indices ranging from HF1 to HF2.