Influence of Phosphorus and Sulphur Segregation on Stress Relief Cracking

Three commercial weldable fine grained structural steels and four experimental melts with lowered contents of trace elements were subjected to a welding simulation treatment followed by stress relaxation (SR) tests. After testing times of up to 8 hours the samples were removed from the testing rig, broken in the fracture stage of an Auger instrument, and the fracture surface was examined in situ for segregation of elements. SEM investigations of the fracture surfaces and light microscope served to characterize fracture mode and microstructure. The microfractural appearance of the grain boundaries exposed by the impact loading in the Auger instrument and of the ones separated by SR-testing was significantly different. While the fracture surfaces originating from SR-testing were flat, the samples subsequently broken in the Auger instrument showed a dimpled structure. It could be shown that cracks always started at MnS - precipitates, and that the intergranular crack propagation was enhanced by the segregation of phosphorus. The segregation of elementary sulphur was initiated by the stress field of the cracks already formed and, contrary to the phosphorus enrichment, could be prevented by lowering the S-content in the melt. The other trace elements seemed to play no part in the stress relief cracking of the steels investigated

Direct Laser Sintering of Metals and Metal Melt Infiltration for Near Net Shape Fabrication of Components

Direct laser sintering of metal powders is a great challenge for Rapid Prototyping (RP) because of the high potential of application, for example prototype tooling for polymer extrusion. Recent development in laser sintering ofmetal powders use polymer or low melting alloys as a binder phase. Postsintering to strengthen the component produces shrinkage ofthe part, hence the near net shape capability is limited. The combination of direct laser sintering and infiltration with metal melts allows the production ofstrong near net shaped components without shrinkage. A composite metal powder consisting ofNi, Cu, Sn and P was successfully sintered in a Selective-Laser Sintering unit in ambient atmosphere at room temperature. The influence oflaser intensity on microstructure and sintering behaviour is discussed. Infiltration experiments were done with partially sintered samples. Full density could be achieved without shrinkage. Mechanical properties and microstructural development will be discussed.Mechanical Engineerin

Untersuchungen zur inhomogenen Scherverformung

Neben den klassischen Werkstoffreaktionen treten inhomogene Scherverformungen bei Impact-Beanspruchungen, Explosionsplattierungen und Überrollvorgängen auf. Im metallografischen Schliff (Stahl) stellt sich diese Erscheinung als schmaler Streifen (10 bis 20 mym) dar, der im Vergleich zum umgebenden Gefüge stark verformt wurde. Auf die Bildung dieser "Weißen Zonen" hat die Verformungsgeschwindigkeit einen entscheidenden Einfluß. Durch einen speziellen Versuchsaufbau (Split-Hopkinson-Bar) konnten diese Scherzonen an definierten Orten in Stählen und Verbundwerkstoffen erzeugt werden. Mit dem REM wurde das Anätzverhalten bei verschiedenen Tiefätzungen untersucht

Verfahren zur Messung der Haftfestigkeit

Bei einem Verfahren zur Bestimmung der Haftfestigkeit einer auf einem Substrat aufgebrachten Beschichtung wird aus dem zu untersuchenden Werkstueck eine Probe in Form einer Platte entnommen, die sowohl den Grundwerkstoff als auch einen beschichteten Teil enthaelt. Diese Probe wird so in einer Aufnahme positioniert und fixiert, dass der Bereich des Grundwerkstoffs auf der Auflage gehaltert wird und dass die Grenzflaeche zwischen dem Substrat und der Beschichtung einer von einem beweglich gehalterten Scherkopf ausgeuebten Scherbeanspruchung ausgesetzt wird. Die zur Abscherung der Beschichtung erforderliche Kraft wird gemessen und daraus die Haftfestigkeit bestimmt

Rapid Prototyping of functional metallic parts

Reducing the time to produce prototypes is a key to speed up the development of new products. Today commercially available Rapid Prototyping systems work with different techniques using paper, polymers and waxes. One big goal in the field of Rapid Prototyping (e.g. in the automotive industry) is the production of metallic prototypes for functional applications and testing. One possibility to produce metal parts is a two step process (production of wax prototypes, e.g. with the Fused Deposition Modeling (FDM) process and subsequently investment casting). The FDM-systern is installed since March 93 at IFAM. Another possibility is the direct manufacturing of metallic components (e.g. stainless steel). A new Rapid Prototyping process which we name Multiphase Jet Solidification (MJS)" is used for this task. Experiences and results with these two techniques are presente

Accuracy and Mechanical Behavior of Metal Parts Produced by Lasesrintering

The work shows the mechanical properties of direct laser-sintered metal parts. The parts were tested after sintering and after an infiltration. Furthermore the accuracy of the parts was measured. Micrographs of the parts show the microstructure of the copper-nicker-tin alloy. The achievable complexity of parts is demonstrated by examples. An overview of future activities is given.Mechanical Engineerin

Schnell von der Produktidee zum Bauteil durch Rapid Prototyping

Flexible production concepts for manufacturing products of high quality require the fast availability of prototypes. Therefore, the processes of Rapid Prototyping (RP) are of great importance. On basis of a 3D CAD description of the geometry to be designed, these new processes often represent the fastest and most economic variant for manufacturing models and prototypes. Tasks of the future are to improve the accuracy and the achievable surface quality of the processes as well as particularly to enlarge the applicable range of materials. The application of RP in the area of mold making is of particular importance. The high demands on molds, e. g. from injection molding up to diecasting, can only be fulfilled by using metallic and ceramic materials. In this paper the procedure from the plastic model to the metallic or ceramic prototype respectively to the mold insert are explained. Direct ways to metallic and ceramic parts and applications of secondary operations are shown