IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Literature data indicate that time to fracture increases with decreasing grain size, reaches a maximum, and then starts decreasing with further decrease in grain size. A constrained cavity growth model has been proposed to explain the above behaviour. This model assumes that the growth and coalesence of isolated cavities on grain boundary facets determines the time to fracture and that this cavity growth is severely constrained by the surrounding creeping matrix. It is also shown that the model prediction compares very well with a set of data valid for an austenitic steel.

Department of Metallurgical and Materials Engineering

Res Mechanica: International Journal of Structural Mechanics and Materials Science

EFFECT OF GRAIN SIZE ON INTERGRANULAR CREEP FRACTURE.

Erosion experiments were carried out on two ductile materials, copper and Cu-6%Al alloy, with an aim to study the dependence of the erosion rate on the impact angle with spherical non-friable steel shot as the erodent. The experiments were carried out at impact angles of 30°, 60° and 90° at an impact velocity of 40 m s-1. The results indicate that the erosion rate is greatest at normal impact for the spherical erodent, in contrast with the general observation that the maximum erosion rate in ductile materials occurs at oblique impact. Scanning electron microscopy examination revealed that lip formation and lip fracture are the operating mechanisms of material removal at all impact angles studied. The experimental findings are rationalized using the localization model. © 1986.

World University root node

Wear

Erosion behaviour of ductile materials with a spherical non-friable erodent

The major objective of the present investigation is to develop empirical procedures for correcting microhardness values for the size effect. Such correction procedures can be expected to be useful in the determination of equivalent bulk hardness values in the highly strained regions just beneath worn or eroded surfaces. In this paper two empirical correction procedures were defined and their usefulness was evaluated on three single-phase materials, namely iron, Cu-2Si alloy and 7075 aluminium. It is found that the hardness subtraction method (one of the two correction procedures) predicts most accurately the equivalent bulk hardness values. Finally, the methodology for converting the corrected microhardness-depth profile beneath a Brinell indentation to an equivalent strain-depth profile is illustrated and the validity of such a procedure is demonstrated. © 1986.

Evaluation of microhardness correction procedures

The major aim of this investigation was to determine the effect of the stacking fault energy (SFE) on the solid particle erosion rate at oblique impact angles. Such an investigation is essential to establish whether erosion is a deformation- or a fracture-controlled process. Towards this purpose, experiments were carried out at an impact angle of 30° on a series of copper alloys with a wide range of stacking fault energies using spherical steel shot travelling at a velocity of 40 m s-1 as the erodent. The experimental results clearly show that the erosion rate decreases with decreasing SFE, thereby indicating that erosion is a deformation-controlled process. An inverse relationship between the erosion rate and the strain-hardening exponent is also observed. In addition, the erosion rate at 30° is lower than the erosion rate at 90°. Finally, it is demonstrated that the localization model for erosion is capable of rationalizing all these observations. © 1985.

The effect of stacking fault energy on the erosion behaviour of copper alloys at oblique impact

An empirical equation relating the volume of the crater formed during high velocity oblique impact tests to the velocity and angle of impact and to the target material hardness has been proposed. It is further demonstrated that this equation can predict the volume of the crater formed quite accurately over a wide range of impact velocities (50-350 m s-1), impact angles (up to 60°) and target hardnesses (1-4 GPa). © 1984.

An empirical relation for the volume of the crater formed during high velocity oblique impact tests

The major objective of the present paper is to study the efffect of stacking fault energy on solid particle erosion and to understand the observed behaviour on the basis of existing erosion models. Towards this purpose, erosion experiments were carried out on a series of copper alloys, with stacking fault energies known to lie in the range 8.8-55 mJ/m2, using spherical hard steel shots at normal incidence and at a velocity of 40 m/s. The results indicate that the erosion rate correlates well with the stacking fault energy and the strain hardening exponent. This correlation as well as absolute magnitudes of the erosion rate are excellently explained by the localization model for erosion. © 1984.

Acta Metallurgica

Correlation between erosion behaviour and stacking fault energy in copper alloys

The existing data on the effect of temperature on solid particle erosion are rationalized in a qualitative fashion by means of the localization model for erosion. It is shown that the temperature dependence of the flow stress of the eroding material and the extent of variation in the strain hardening exponent with temperature largely determine the influence of temperature on erosion rate. © 1984.

The effect of temperature on solid particle erosion

The essential features of erosion are reviewed with emphasis on results of TEM/SEM observations carried out on eroded surfaces. The flow behavior of the target material under erosion conditions (high strains, high strain rate) is considered. Erosion models are described and their ability to explain the phenomenological aspects are explored.

Transactions of the Indian Institute of Metals

SOLID PARTICLE EROSION OF METALS AND ALLOYS.

A new theoretical model is proposed for the erosion of metals by particles at normal incidence. The model employs a criterion of critical plastic strain to determine when the material will be removed. This critical plastic strain is defined as the strain at which the deformation in the target localizes and hence results in the lip formation. It is shown that, under typical erosion conditions, the "localization" model is more appropriate than the "fatigue" models. Finally, it is demonstrated that the new model predicts quite well all the essential features of the normal impact erosion process. © 1983.

A new model for the erosion of metals at normal incidence

Localized lip formation and subsequent lip fracture is the dominant mechanism by which material is removed during the normal incidence of single spherical particles on ductile targets. A theoretical model which predicts the extent of lip formation as well as the weight loss during these single impact experiments is presented. The model postulates that the lip formation is the result of localization of deformation in the near-surface regions of the target and that the lip is removed either by inertial-stress-induced tensile fracture or by separation across adiabatic shear bands formed at the base of the lip. The single-impact data for copper, brass, thoria dispersed (TD) Nickel and nickel targets are shown to compare very well with the predictions of the model. © 1983.

An analysis of the localization of deformation and weight loss during single-particle normal impact

This paper deals with erosion processes involving particles much harder than the target, which are borne against the target at velocities of tens to hundreds of meters per second. The authors are concerned with answering four questions fundamental to understanding erosive metal loss, namely, 1. How do lips or platelets form? 2. What criteria must be met for the removal? 3. What role, if any, does the local temperature rise accompanying impact play in metal loss? 4. What is the role of embedded abrasive particles in the erosion process?

Annual Review of Materials Science

EROSION OF METALS.

The deformation of a metal target under an impacting hard elastic ball is analyzed to show that simple measurements can lead to valid stress-strain and stress-strain rate data. It is found that pure metals, exhibit the highest strain rate sensitivity while the solid solution alloys show intermediate strain rate sensitivity. On the other hand, in the case of precipitation hardened and dispersion strengthened alloys, the flow stress is insensitive to strainrate. The observed strainrate effects are rationalized in terms of a three component flow stress model incorporating the athermal, thermally activated and viscous components. © 1983.

The use of dynamic impact experiments in the determination of the strain rate sensitivity of metals and alloys

This paper presents a model for the kinetics of growth of methane bubbles. The model considers two parallel processes which can control the growth - one involving bubble growth by direct power-law creep and the other involving combinations of surface diffusion, grain boundary diffusion and matrix accommodation processes.

Metallurgical transactions. A, Physical metallurgy and materials science

KINETICS OF HYDROGEN ATTACK OF STEELS.

Three high strength low alloy steels with low carbon contents and varying alloy contents were exposed to 21 MPa (3000 psi) hydrogen pressure in the temperature range 350 to 510°C. The resulting sample expansion rate was measured using a highly sensitive capacitance dilatometer. In all three HSLA steels, the early expansion rate was found to be independent of exposure time, but a function of exposure temperature and pressure. The temperature dependence of the sample expansion rate was similar for all three HSLA and the reference carbon steels, and corresponded roughly to an activation energy (Q) of 190 KJ/mole. The later accelerating expansion rate fitted a Q of 160 KJ/mole. Though the sample expansion rates exhibited the same temperature dependence, they varied by as much as two orders of magnitude among the three HSLA and the carbon steels. This marked variation in rate was proportional to the estimated carbon activity in each steel. Comparison between the Nelson curves published by the Americal Petro-leum Institute (API) for 1/2 pct Mo steel and the experimental curves constructed for HSLA steels indicated that these steels should provide comparable or better resistance to hydrogen attack than the 1/2 pct Mo steel. © 1980 American Society for Metals and the Metallurgical Society of AIME.