Role Of Surface Conditions Research Articles

Failure behavior of resistance spot welded advanced high strength steel: The role of surface condition and initial microstructure

The continuous galvanizing process (CGP) under high dew point temperature has been recognized as a viable technique for improving the coating quality of advanced high-strength steels (AHSS). However, the effect of this surface modification technique on resistance spot welding (RSW) process is not clear. The aim of this study is to investigate the role of different surface conditions and initial microstructures obtained through CGP on mechanical properties and failure behavior of resistance spot welded AHSS. It has been shown that the formation of internal oxides during the annealing and subsequent coating process reduced the heat input during RSW, resulting in smaller nugget size and consequently, lower tensile-shear peak load values. Finite element modeling (FEM) and experimental results indicated that in the case of the as-received sample, higher fusion zone/base-metal (FZ/BM) hardness ratio leads to a failure location closer to heat-affected zone (HAZ). However, the lower FZ/BM hardness ratio in the case of annealed-bare and annealed-coated specimens leads to failure location more towards FZ. It was shown that nugget size will not control the failure location during lap-shear loading but does affect nugget load-carrying capability. However, failure behavior is controlled by microstructural characteristics of different weld regions.

Emissivity of Grade 91 Ferritic Steel: Additional Measurements on Role of Surface Conditions and Oxidation

Measurements and data are reported for the total hemispherical emissivity of Grade 91 steel [ASTM International (ASTM) A387 Grade 91] for the temperature range of 400 K to 1048 K using ASTM standard C835-06. The surfaces studied included (1) an electric discharge machining (EDM) cut, (2) Grade 91 steel sandblasted with 320-grit-sized alumina beads, (3) EDM-cut Grade 91 steel oxidized in air, and (4) Grade 91 steel sandblasted with 320-grit-sized alumina beads and oxidized in air. The EDM-cut Grade 91 steel was oxidized at 873 K and 1023 K for 1, 3, and 5 h. The 320-grit sandblasted Grade 91 steel was oxidized at 1023 K for 5 h. Air oxidations were carried out in a three-zone furnace at fixed airflow. It appears that under some conditions, Grade 91 steel can reach the emissivities required for passive heat removal during an air ingress accident.

Adhesion Force between a Silver Particle and Haynes 230: Role of Surface Conditions

A methodology is developed to measure the adhesion force and the work of adhesion between aerosols generated in very-high-temperature reactors (VHTRs) and interacting with structural materials. The method uses an interactive system of a silver particle interacting with Haynes 230 (H230) surfaces, compares the measured data with theoretical values, and uses an atomic force microscope in an air environment glove box with ambient temperature of 20.27°C and relative humidity of 34.97%. The adhesion force data are obtained for a silver particle interacting with H230 under four different surface conditions including “as received” and after oxidation for 5, 10, and 15 min, respectively. It was found that the JKR (Johnson-Kendall-Roberts) theory predicted values that were up to three orders of magnitude higher than the experimental data. In contrast, the inclusion of surface roughness from both the particle and H230 samples in the calculations produced results that are one order of magnitude higher than the experimental data. These comparisons provide insight into the significant influence that surface roughness has on adhesion force. A range of values of 0.02 to 0.3 μN was obtained from the adhesion force distributions of measured data that can be used as bounds on forces that can be produced in a silver-H230 interactive system.

The Role of Surface Condition in the Yields of Secondary Electrons, Backscattered Electrons, and Photoelectrons From Spacecraft

This paper reviews some active research topics of outgoing electron currents in spacecraft charging. The spacecraft potential is determined by the current balance. On a spacecraft, the incoming currents of ambient electrons and ambient ions can be measured, whereas the outgoing currents of secondary electrons (SEs), backscattered electrons (BEs), and photoelectrons (PEs) cannot. The outgoing currents depend on the incoming currents, surface materials, and surface conditions. For SE yields, using the encyclopedia parameters of the materials is not sufficient; surface conditions also need to be taken into account. For BEs, the yield approaches unity as the primary electron energy approaches zero. For PEs, reflectance is important. We conjecture that highly reflective surfaces generate little or no PEs and would charge to negative voltages as if in eclipse. As a consequence, differential charging may develop between adjacent surfaces as they get exposed to sunlight.

The effect of manufacturing variables on the corrosion resistance of a super duplex stainless steel

Recent in-service failures of super duplex stainless steel (SDSS) components have revealed the important role of manufacturing variables on the corrosion behaviour of the material. These variables include surface condition, heat treatment and cold work. The effect of all three variables on the corrosion behaviour of an example SDSS was investigated using electrochemical techniques, tensile testing and microscopic observations. The role of surface condition was investigated by characterising the topography of specimens using the surface roughness parameter, R a, then measuring the critical pitting temperature. The results showed that R a on its own is not sufficient to characterise the effect of surface condition on corrosion resistance. The effect of heat treatment on pitting potential was pronounced as a result of the intermetallic phases precipitated. Plastic deformation caused by cold work affected the pitting potential of the material, although the effects varied with increasing cold work; certain plastic strain levels caused reduced resistance, whilst others caused little change compared with the solution-annealed specimens. Hydrogen embrittlement increased with increasing cold work. The main conclusion is that the interactions between corrosive environments and SDSS components containing one or more of these manufacturing variables must be considered if reductions in service life are to be avoided.

The surface tension of liquid aluminium in high vacuum: The role of surface condition

Despite the fact that aluminium is one of the most widely used metals, there is still a great uncertainty, of the order of 25%, on the intrinsic value of its surface tension σ. The origin of this large dispersion, which is much higher than the typical error of σ measurements (2–3%), is undoubtedly the high sensitivity of surface properties of molten Al to oxygen. In the present study the question of the surface tension of pure Al and its relationship to the surface condition is discussed in the light of new surface tension results obtained by employing an accurate technique (the “large drop” technique) that minimizes the experimental error on σ, and high vacuum/high temperatures to promote deoxidation of molten Al.

High temperature cross-weld characterisation of steel weldments by microtensile testing

Study of local material properties and damage mechanisms are undertaken in order to characterise weldments that show significant variation of properties across weldments. One of the methods to characterise the local variation of properties is microtensile (MT) testing of specimens machined out of specific narrow zones of weldments. The literature data, though limited, on microtensile specimen testing are reported at their low temperature behaviour. On the other hand, systematic study of crossweld local material properties at high service temperatures have not yet been reported. In the present study, MT tests are conducted across similar welds of P22 and P91 steels at 550 and 600°C, respectively. In order to study deformation mechanisms and the role of surface condition on properties, specimens with different surface conditions (i.e. machined, polished and electropolished surfaces) are tested. Two different loading rates of 0.2mm/min and 0.5mm/min are used to study the effect of loading rate on deformation and mechanical properties. Variations of material properties yield strength (Rp0.2) and ultimate tensile strength (Rm), for the weldments are presented as a function of surface conditions of specimens and loading speeds. Higher loading rates yield higher values of Rp0.2 and Rm, and specimens with machined and polished surfaces show consistent and higher values of Rp0.2 and Rm compared to specimens with an electropolished surface finish. Deformation behaviour is studied on the side surfaces of tested microtensile specimens using an SEM. Deformation is correlated to microstructural constituent that is observed on specimen side surfaces. The metallographic information is used to interpret the variation of mechanical properties determined in tension at high temperatures. The MT data are compared with standard tensile data obtained on specimens with simulated microstructures. The prospects of using MT tests for characterising the material at high temperatures and feasibility of use of data for assessment of components under service loading conditions are reported.

The role of surface condition, residual stress and microstructure on pre-yield cracking in Ti44Al8Nb1B

Fully lamellar and duplex samples of Ti44Al8Nb1B, with a range of surface treatments, have been tested in tension using acoustic emission to detect the onset of pre-yield cracking. The magnitudes and the senses of the stresses left in the surface regions of machined, polished and annealed samples have been measured using synchrotron radiation and these measurements correlated with the minimum level of the applied stress at which cracking was detected. The observations have shown that the surface condition is far less significant than the microstructure in determining when cracking is first observed and that, whatever the surface condition, the duplex structure never shows detectable pre-yield cracking. These results are discussed in terms of the mechanism which leads to pre-yield cracking and its role in limiting fatigue life.

Influence of surface treatment on creep behaviour of NiAl single crystals

Abstract Stoichiometric [110] oriented NiAl single crystals were deformed by compression creep tests at 300 °C up to 3.6%. To ascertain the role of surface conditions, deformation samples with mechanically polished, rough and oxidised surfaces were used. The polished samples were most easy to deform. An oxide layer of about 600 nm thickness did not give rise to softening due to poor oxide adherence. The dislocation substructure in the bulk and near the surfaces was investigated by TEM. The different arrangements were discussed with regard to dislocation generation at the surfaces, cross-slip and mutual annihilation of screw dislocations and edge dislocation trapping to form dipoles.

The role of surface conditions on fatigue behaviour of metal parts: Lieurade, H.-P. Surfaces Sept. 1989 27, (208), 70–71, 74, 77–78, 80 (in French)

Measurements of the permeation rate of deuterium in martensitic steel DIN 1.4914 (MANET) were performed by a gas permeation technique over the temperature range 560–740 K and for deuterium driving pressures in the range from 9 to 5 × 104 Pa. From these measurements, the surface constants for the adsorption (σ-κ1) and release (σ,κ2) of deuterium in MANET were determined. The experimental values of the surface constants σκ1 and σκ2 are well described by the following equations: σ k1= 7.66 × 10−6 exp (−55217/RT) (mol m−2 Pa−1 s−1), σκ2 = 2.59 × 10−5 exp (5781/RT) (mol−10 m4 s−1), where R = 8.314 J K−1 mol−1 and T is the temperature in Kelvin.

Seismic Risk and Mountain Environments: The Role of Surface Conditions in Earthquake Disaster

The paper examines the extent to which damages in earthquake disasters depend upon features of mountain land environ- ments and human settlement of them. The damage zones of nine out of ten major disasters in recent decades involve mountainous areas. Destructive failure of steep slopes is one recurrent, globally significant indicator of the role of mountainous terrain. Weather and problems of access relating to mountain extremes and terrain are also frequent and serious problems for survival and relief in disaster. It was also found that many of the detailed problems stem from, or have been magnified by, recent ecological and societal changes in the mountains. However, it is the mountain foot and mountain fringe areas where the greatest extent and concentrations of damage occur. Patterns of damage in most earthquake disasters accord with patterns of mountain foot settlement, the complex environment of piedmont ecotones and land uses. Herein lies much of the explanation for geographical concentrations of the disasters in drier lands and coastal settings. Pressures of recent insensitive ecological and social change in these areas, where there are sharp and sudden contrasts in susceptibility to seismic shaking, seem to be a major factor in many of the damages recorded.

N, p and n, np reactions with 14 MeV neutrons

Measurements of the energy spectra of protons emitted in n, p and n, np reactions with 14 MeV neutrons are described. The spectra are taken at four different angles in the case of Ni, Cu, Mo, and Ag. The results are compared with other results in the domain of the nuclear reactions at intermediate energy. The mechanisms responsible for the various reactions can be shortly indicated: 1) instantaneous effects: the forward emitted high energy particles are due to such effects. 2) non equilibrium escape is responsible for the main part of the spectra and for emission at any angle. The escape is supposed to be due to the strong interactions between few excited nucleons at the nuclear surface; 3) retarded emission, probably after stabilized equilibrium is reached, will explain the emission of protons by mediumA nuclei and of neutrons when incident energy is below 18 MeV. Values of temperatures of ∼ 1 MeV are found. In n, 2n and n, np reactions strong emission of protons competes in some cases with neutron emissions. The role of surface conditions in this retarded emission is enlightened.