WEAR PROPERTIES OF FE-CUC BASED MATERIALS PRODUCED BY POWDER METALURGY
In this study, Fe-Cu-C based compact in various weight ratios of iron, copper and graphite additions to starting powder have been produced by powder metallurgy. The effects of copper and graphite additions and sliding speeds during wear tests on wear behaviours were investigated. In this study, wear tests were carried out by using pin on disc sliding wear machine with the sliding speeds of 1, 1,5 and 2 msn at the constant loads of 20N. 2000 m total sliding distance was selected. Scanning Electron Microscopy (SEM) studies were carried out on the cross section of the compacts. Worn surfaces of the samples after tests were also examined by using scanning electron microscope and energy dispersive spectroscopy (EDS) analyses. The results obtained from experimental work shows that addition of copper and graphite and sliding speed effect on wear behaviours of sintered alloyed steel materials.
Dry sliding wear behavior of molybdenum alloyed sintered steels
Abstract Powder metallurgy (PM) steels of the composition Fe–3.5% Mo–1.0% C were prepared by pressing and sintering, and the wear behavior of the steels was investigated. Through wear test combined with SEM surface analysis and metallurgical analysis of the specimens showed that the wear behavior of these steels depends on the PM processing parameters and the heat treatment as well as on the wear conditions. Specimens quenched and tempered at 500°C have high wear coefficient compared with specimens as-sintered. At sliding speeds of 1 to 5 m s−1 and normal loads of 10 to 30 N, the PM steels have low and stable wear rate. The wear mechanisms are oxidation wear, adhesive wear, abrasive wear and melt wear depending on the wear conditions.
Live birth in the Devonian period
The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.