Interfacial precipitation in hot isostatically pressed diffusion bonds of 17-4 PH stainless steel

Abstract

The embrittlement of hot isostatically pressed (hipped) diffusion bonds manufactured from 17-4 PH stainless steel has been investigated by Auger electron spectroscopy (AES) of in situ fracture specimens. Depth profiling by AES has revealed copper precipitation at the interface of the diffusion bond. This precipitation, up to a few monolayers in thickness, occurs during the ramp up to temperature and pressure of the hot isostatic pressing (hipping) cycle and is not readily removed by subsequent heat treatment. This effect is explained in terms of the metallurgical characteristics of copper within the steel. Results suggest that the extent of the precipitation decreases with increasing process temperature. In the case of PH 13-8 Mo stainless steel, where the precipitation hardening phase is NiAl, the interface is weakened by sulphur segregation and the formation of oxide particles.     

Influence of hot rolling and heat treatment on structure and properties of HSLA steel explosively clad with austenitic stainless steel

Abstract

The present work aims at studying structure–property correlations in an explosively clad HSLA steel with austenitic stainless steel of AISI 304L grade. The clad plate was subjected to hot rolling followed by a quenching and tempering treatment to achieve better mechanical properties in the base plate. Optical microscopy studies revealed that the interface between the two steels was wavy in the as clad plate and the waviness decreased substantially due to hot rolling. Subsequent heat treatment has not shown any significant effect either. The base plate had tempered martensite/bainite structure in as clad or heat treated conditions and ferrite-pearlite-bainite structure in hot rolled condition. The grains were finer and elongated near the interface. The stainless steel exhibited equiaxed grain structure in as clad, hot rolled or heat treated plates. Tensile properties and charpy impact energy of the base plate were lowered due to hot rolling and then increased substantially due to heat treatment. The microhardness was observed to be a maximum at the bond interface for all three conditions studied. The shear bond strength was the highest in the as clad condition and decreased for the rolled as well as heat treated conditions. Scanning electron microscopy fractography on shear bond specimens revealed the presence of predominantly equiaxed dimples with few regions of rubbed fracture. Quantitative electron probe microanalysis across the bond interface indicated linear change in concentrations of nickel, chromium and manganese between the levels appropriate to the clad layer and base metal.     

Influence of thermomechanical processing on superplastic forming of Mg–Al alloys

Abstract

The aim of this paper is to study the influence of the initial microstructure of several Mg–Al alloys on their superplastic formability and on their post-forming microstructure and mechanical properties. Various thermomechanical processing routes, such as annealing, conventional rolling, severe rolling and cross rolling, were used in order to fabricate AZ31 and AZ61 alloys with different grain sizes. These materials were then blow formed into a hat shaped die. It was found that the processing route has only a small effect in the formability of Mg–Al alloys or on the post-forming microstructures and properties due to rapid dynamic grain growth taking place at the forming temperatures. Nevertheless, good formability is achieved as a result of the simultaneous operation of grain boundary sliding and crystallographic slip during forming.     

MECHANICS ANALYSIS ON PRECISE FORMING PROCESS OF EXTERNAL SPLINE COLD ROLLING

According to the suitable assumption, the deformation process of external spline cold rolling is analyzed. By the graphing method, the slip-line field of plastically deforming area in process of external spline cold rolling is set up. Different friction-conditions are used in different contact areas in order to realistically reflect the actual situation. The unit average pressure on contact surface of the rolling process is solved according to the stress filed theory of slip-line. And the formulae of the rolling-force and rolling-moment are established. The theoretical result is well consistent with the finite element analysis. A theoretical basis is provided for the precise forming process of spline cold rolling and the production of external splined shafts.     

Engineering nanostructured thermal spray coatings: process–property–performance relationships of ceramic based materials

Abstract

Nanostructured powders were deposited using thermal spraying to produce coatings having internal features of nanosized dimensions. Several ceramic based materials were studied, including WC–12 wt-%Co, TiO₂, hydroxyapatite, Al₂O₃–13 wt-%TiO₂ and yttria stabilised zirconia. The effect of the thermal spray conditions on the microstructure, phase composition, properties and performance was investigated. Key nanostructural features of the coatings were identified and their potential benefit in contributing to enhanced behaviour explored. Issues relating to design strategies and process control for engineering these types of coatings with performance characteristics tailored for targeted applications are discussed.     

New parameters for the description of hot rolled strip transverse temperature distribution: preliminary applications

Abstract

Nowadays, it is possible to find experimental data about the longitudinal temperature distribution for a hot rolling strip production. However, it is much more difficult to obtain experimental results on the transverse temperature distribution on the strip surface. After a systematic analysis of the methods and results in the literature, the experimental data collected using a specific experimental apparatus to measure the transverse strip temperature distribution out of the last finishing stand of a 1800 mm wide thin hot strip rolling mill are presented. In order to logically classify all the results by identifying the main factors that influence the strip temperature profile, it is proposed to describe more clearly four new parameters of the strip thermal profiles which would allow the investigation of the reason for uneven transverse temperature distributions. The relationship between strip temperature distribution, strip geometry and temperature itself is also studied to provide a basis to build a mathematical model for the current problem.     

Powder reaction mechanism in fabrication of high silicon iron alloy

Abstract

In the present paper, the reaction mechanism of silicon and iron powders under different sintering conditions during the fabrication of high silicon iron sheet (～6·5 mass-%Si) is clarified. It is indicated that the phases, Fe₃Si (Si) and FeSi, play an important role in the reaction between iron and silicon powders. Two temperature regions of the powder reaction are very important for producing commercial high silicon iron sheets: the temperature region of ～1000°C in which the ductile composite structure can be produced, and the temperature region of ～1200°C in which the density and homogeneity can be improved.     

Properties of ausformed austempered ductile iron (AADI) containing Ni

Abstract

The abrasion wear behaviours of Ausformed Austempered Ductile Iron (AADI) and conventional Austempered Ductile Iron (ADI) were investigated. The effects of both Ni content and rolling reduction during the ausforming process on the wear resistance of AADI and ADI were studied. The ausforming process created a finer and more homogeneous ausferrite structure that had a direct influence on the mechanical properties of AADI. Maximum hardness and tensile strength were obtained with 35% rolling reduction. On the other hand, ductility and impact strength were reduced with increasing rolling reduction during the ausforming process. AADI showed superior abrasion wear resistance because of its finer and harder structure.     

Measurement of grain size and size distribution in engineering materials

Abstract

Methods to characterise grain size distribution in engineering materials are evaluated, and compared with measurements on two representative materials, an equiaxed aluminium alloy and a heterogeneous nickel alloy. Computer simulations from a model tetrakaidecahedron structure have also been obtained using a personal computer program to rotate and section the model randomly, generating distribution data on section area and intercept lengths. Comparisons have been made between the model distribution data and intercept distribution data from the material microstructures.

It is recommended that size distributions of area plotted against size (intercept) or normalised size provide an effective method for discriminating between different grain size distributions. An estimate of area can be used indirectly by squaring intercept values rather than making direct measurements of grain areas.     

Integration of vision and walking skills together with high-level strategies for quadruped robots to play soccer

Legged robots taking part in real multi-agent activities represent a very innovative challenge. This domain of research requires developments in three main areas. First, without any feedback information from the environment, there is no way for robots to achieve some tasks autonomously. Fortunately, the quadruped 'Sony' prototypes on which all experiments are carried out are equipped with an enhanced vision system; thanks to its CCD camera located in its head, the robot can obtain color images of the scene around it. Extracting relevant information from the images captured is not easy since it must be done onboard in real time. Moreover, image treatment procedures should have high process rates for the robot to react quickly in front of unexpected events. A special vision module composed of three parts has been designed for these purposes. The second point to focus on is the walking ability of the robot. Quadrupeds are designed to move efficiently and rapidly on flat ground. The objective of the walking module is to generate appropriate walking patterns allowing the machine to walk in the desired direction. Walking gaits are produced like reflexes by the robot itself to adapt to the situation. With regard to the design of these gaits, emphasis has been put on increasing speed and mastering transitions. Finally, the machine should be given a minimum of intelligence since it has to manage vision information and its walking gaits by itself. When involved in situations of cooperation or competition or both, like in a soccer game, a high-level supervision task is welcome. This paper presents detailed developments of these three points and describes how they are implemented on a real robot.