Surface finish generated in hard turning of quenched alloy steel parts using conventional and wiper ceramic inserts

Significant progress has already been achieved in green manufacturing including dry and hard, often high-speed, machining technologies. For instance, the demand for higher productivity has resulted in the wider application of ceramic and PCBN tools with special multi-radii (wiper) geometry. This paper reports some important characteristics of the surface roughness produced in the turning of a hardened low-chromium alloy steel using mixed alumina–titanium carbon (TiC) ceramic cutting tools equipped with both conventional and wiper inserts. The characteristic geometrical features of surfaces obtained in both these turning operations have been assessed by means of representative two-dimensional (2D) surface roughness parameters, and some 3D visualizations, which allowed more complete characterization of the surface topography and prediction of its service properties. Results show that keeping equivalent feed rates, i.e. 0.1 mm/rev for conventional and 0.2 mm/rev for wiper tools, the surfaces obtained have similar 3D height roughness parameters, and comparable values of skew and kurtosis. At defined cutting parameters, surfaces produced by wiper tools contain blunt peaks with distinctly smaller slopes resulting in better bearing properties. Only marginal changes of Ra parameter were recorded during 15 min machining trials.     

Role of platinum in the Na2SO4-Induced hot corrosion resistance of aluminum duffusion coatings

Electrochemical corrosion measurements have been carried out with Pt-containing and Pt-free Al-diffusion coatings on IN 738 LC in a 90Na₂SO₄+ 10K₂SO₄ (mol%) melt at 1173 K. Pt improves the resistance to basic fluxing while there are no significant differences between both coating types in their resistance to acidic fluxing. The corrosion resistance of the Pt-containing coating is also higher in the passive potential region where protective scales rich in Al₂O₃ are formed. The reason for the different behavior of both coating types appears to be related to the high corrosion resistance of the Pt-rich surface layer of the coating and an increased Al₂O₃ content in the scale of the Pt-containing type.     

Suppression of carbon monoxide formation in oxide-coated TZM molybdenum X-ray rotating anodes

Higher performance designs for rotating anode X-ray tubes have increased the average rotating anode temperature from below 1100 °C to well above 1300 °C. This temperature increase has accelerated the formation of carbon monoxide by reaction of carbon from the alloy substrate with oxygen from the emissive coating. The dominant carbon source is thought to be Mo₂C grain boundary precipitates in the TZM molybdenum alloy substrate. The dominant oxygen source is thought to be TiO in the emissive coating. Placement of a monocarbide-forming reactive layer between the alloy substrate and the emissive coating has been demonstrated to lower the thermodynamic activity of the carbon source and dramatically reduce the rate of formation of carbon monoxide.     

Issues in the replacement of lead-bearing solders

The use of soft solders, particularly those containing lead, dates back nearly 5,000 years. Solders similar to the materials used to seal the aqueducts of ancient Rome are now an important building block in the manufacture of high-speed computer assemblies. This history attests to the technological versatility of soft solders and, in particular, the solder alloys that contain lead. However, the health effects of prolonged exposure to lead have also been documented; measures to limit human exposure—at the work place and indirectly through the environment—are being considered. The successful introduction of lead-free solders into future electronic products will rely heavily upon their solderability, which can be evaluated by test procedures such as the meniscometer/wetting balance technique and the capillary flow test.     

Microstructural Investigation of Protective and Non-Protective Oxides on 11% Chromium Steel

FIB, SEM and STEM/EDX were used to investigate X20 stainless-steel samples exposed to dry O₂, or O₂ containing 40% H₂O, with a flow velocity of 0.5 cm/s or 5 cm/s, for 168 hr or 336 hr at 600°C. Thin protective Cr-rich (Cr,Fe)₂O₃ was maintained on the samples exposed to dry O₂, even after 336 hr, and on the sample exposed to O₂/H₂O mixture with the low-flow velocity (0.5 cm/s) for 168 hr. The oxide scale formed in the latter environment contained less Cr, due to Cr loss through CrO₂(OH)₂ evaporation. Breakaway oxidation occurred on the samples exposed in high-gas-flow velocity for shorter time (168 hr) or in low-gas-flow velocity (0.5 cm/s) for longer time (336 hr). The breakaway scales featured a two-layered structure: an outward-growing oxide “island” consisting of almost pure hematite (α-Fe₂O₃), and an inward-growing oxide “crater” consisting of (Cr,Fe)₃O₄. The transition from a thin protective (Cr,Fe)₂O₃ scale to a non-protective thick scale on this martensitic/ferritic steel originated locally and was followed by rapid oxide growth, resulting in a thick scale that covered the whole sample surface.     

Experience in chemical heat treatment of parts made of powder materials for vaz passenger cars

Every car of the Volzhskii Automobile Plant consists of 1.6 (VAZ-2106) to 4.0 (VAZ-2110) kilograms of parts fabricated from powder materials. By the middle of 1996 the range of these parts (weighing from 1.5 to 600 g) consisted of 150 items. They are fabricated from powders based on iron and copper (119 and 31 items, respectively). Almost half of the iron-base powder parts are subjected to various kinds of surface treatment, namely, carburizing, cyaniding, gas nitriding, and steam oxide treatment. The present paper is devoted to the special features of chemical heat treatment (CHT) of parts produced from iron (steel) powder materials.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 18–21, October, 1996.     

Crystal structural refinement of the new compound TmAlB14

Single crystals of the new phase TmAlB₁₄ were grown using the high-temperature solution method. The crystal structure of TmAlB₁₄ was refined from X-ray powder diffraction data using the Rietveld method. The structure is of MgAlB₁₄-type with the space group Imma and unit cell parameters a = 5.8212(3) Å, B = 10.3837(2) Å and C = 8.1762(3) Å. The final, conventional R-valve and profile R-value are 0.031 and 0.064, respectively. The structure is characterized by a partial occupancy of both metal positions and a splitting of the thulium atomic position.     

Mechanical properties and fracture upon static tension of the high-carbon steel with different types of pearlite structure

The hardness and mechanical properties of the U10 steel (1.03 wt % C) with pearlite structures that were formed by isothermal decomposition at temperatures of 650°C (coarse-lamellar pearlite) and 500°C (fine-lamellar pearlite) as well as upon subsequent annealing of fine-lamellar pearlite at a temperature of 650°C for 10–300 min have been studied upon tensile tests. Fractures of the steel with different types of pearlite structure have been examined using scanning electron microscopy. The interrelation between the mechanical properties and the structural features and character of fracture has been analyzed for this steel with pearlite structures differing in the dispersity, morphology, and defect structure of cementite, and in the levels of solid-solution strengthening and microdistortions of the ferrite-constituent lattice.