Damaged Surface Region Research Articles

Synchrotron microtomography of supported catalysts

Synchrotron microtomography is a new technique which is capable of elemental, chemical, and structure sensitive imaging in three dimensions at resolutions better than 15 μm. This paper describes the first application of this new technique to the investigation of the morphology and elemental distribution of a supported catalyst. Using this new tool it was possible to obtain three-dimensional information from regions of the catalyst away from the vicinity of the damaged surface region of the sample. The technique allows the use of both computed tomographic (CT) cross sections as well as the development of a three-dimensional rendering of elements in a material, each of which allows visualization of different areas that would go unnoticed in normal radiographic or CT investigations.

Enhanced Diffusion in Boron Implanted Silicon

not Available.

Stoichiometry effects at NiMo surfaces under bombardment with Ar + ions from 40 to 2000 eV

The stoichiometric variations at and below the surface of a polycrystalline 79.2Ni-20.8Mo alloy being induced by normal bombardment with Ar + ions of 40 to 2000 eV have been investigated with AES. A special plasma arrangement was used as a laterally homogeneous ion source. The depth dependent compositional variations in the uppermost atomic layers are derived from the different behaviour of the individual Auger peaks as a function of the energy of bombarding ions. The sputter induced elemental depth distributions are, additionally, sputter depth profiled with 50 eV Ar + ions. The elemental concentration profiles display a pronounced enrichment of the Mo component in the damaged surface region. With increasing E 0 the maximum of the bombardment induced Mo concentration profile is shifted to a distance up to several atomic layers below the surface. The results supply not only detailed information on bombardment induced stoichiometric changes with depth, but also on the size and the shape of the atomic collision cascades in sputtering.

State of the subsurface region in machining-solution-treated and aged 18% Ni maraging steel

The effect of cutting speed and tool wear land length on the mechanical and metallurgical state of the subsurface region of solution-treated and aged 18% Ni maraging steel machined under unlubricated and lubricated orthogonal conditions was determined. The surface region of machined test pieces was examined using optical microscopy, X-ray microprobe analysis, plastic strain analysis and microhardness measurements. Tool forces were measured. The results of the investigation show that when machining under unlubricated conditions, a very narrow (damaged) surface region is produced that is different from the bulk of the material. At low cutting speeds the damage consists of hardening associated with plastic deformation whereas at high cutting speeds the damage consists of thermal softening associated with overaging. When machining under lubricated conditions, very little surface region damage is produced. The results are interpreted in terms of the interaction between the tool nose region and freshly machined workpiece surface.

Surface Integrity in Machining AISI 4340 Steel

The effect of cutting speed and tool wear land length on the surface integrity of quenched and tempered AISI 4340 steel machined under dry, unlubricated orthogonal conditions is determined. The surface region of machined test pieces is examined using optical microscopy, scanning electron microscopy, X-ray microprobe analysis, microhardness measurements, and profilometry. In addition, tool forces are measured and tool temperatures calculated. The results of the investigation show that during machining a damaged surface region is produced which is quite different from the bulk of the material. It is found when cutting at low speeds with sharp cutting tools that the damage is restricted to a variety of geometrical defects associated with the surface. It is found when cutting at high speeds or with tools having large artificially controlled wear lands that considerable subsurface damage involving changes in metallurgical structure and hardness is produced. The results are interpreted in terms of the type of chip produced during machining, the temperatures generated during machining, and the interaction between the tool nose region and workpiece. It is suggested that observations based on scanning electron microscopy are more indicative of the true surface condition than surface roughness measurements.

Behavior of magnetophotoconductivity of semi-insulating GaAs upon α-particle bombardment

The effect of 2-MeV α-particles on the magnetophotoconductivity of semi-insulating GaAs single crystals mounted in the Voigt geometry has been investigated at 300°K. Upon bombardment of the specimen we found an increase of the positive branch of the magnetophotoconductivity while the negative branch remained unaltered. The increase is attributed to a decrease of carrier lifetime in the damaged surface region. The negative branch remains constant since the α-particles do not influence the bulk properties.