Lars Nyborg

Surface chemical analysis of prealloyed water atomised steel powder

Abstract Prealloyed water atomised steel powder was investigated regarding composition, morphology and thickness of the surface oxide. The materials were two varieties of Cr alloyed and one Mo alloyed. The oxides formed on powder surfaces were studied by means of the surface analytical techniques X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy, in combination with high resolution electron microscopy and X-ray microanalysis. On all powder surfaces, the oxide formed contained strong oxide forming elements such as Cr, Mn and Si. Still, the dominant oxide on the powder surface was Fe oxide, the relative cation concentration in the surface being about 80%. The surface morphology showed a heterogeneous structure with particulate compounds supposed to be rich in strong oxide formers and an Fe rich thin oxide layer. This heterogeneous surface oxide morphology was more pronounced for the Mo alloyed powder compared with the Cr alloyed varieties. For this alloy, the average thickness of the oxide layer was somewhat larger (7–87·5 nm for fraction , <63 μm and 63–106 μm) compared with that of Cr alloyed powder (6–7 nm in all cases for fraction , <63 μm and 63–106 μm). An interesting observation was that Cr oxide also appeared on the nominally Cr free Mo alloyed powder, which indicates selective oxidation of Cr also when this element is present in low quantities. Although the alloying elements are enriched by a factor of 40–50 in the surface oxide, there is little effect on depletion of them from the steel matrix. From a sintering point of view, the particulate oxide compounds should play a minor role, since the most probable contacts between individual metal particles are Fe oxide/Fe oxide.

Study of reaction process on Ni/4H–SiC contact

Abstract The present study deals with mechanisms of the reaction process of fabricated thin film Ni/SiC contacts by means of XRD, XPS and Raman spectroscopy. After annealing SiC samples sputter coated with Ni at 800 and 950°C in vacuum for 20 min, the dominant silicide is textured Ni2Si. Its formation consists of two stages: initial reaction rate and subsequent diffusion controlled stage. For ultra thin initial Ni layer (∼3–6 nm), islands formation of Ni2Si is observed after heat treatment. Increasing the Ni film thickness prevents this phenomenon. The C released owing to the Ni2Si formation reaction forms a thin graphite layer on the top of the surface and also tends to form cluster inside the reaction layer. The overall degree of graphitisation is higher at 950°C than that at 800°C.

Inverse identification of flow stress in metal cutting process using Response Surface Methodology

In this study, a methodology was presented to determine the flow stress behaviour of the work material within the range of strain, strain rate and temperature encountered during chip formation process by means of inverse modelling of orthogonal cutting operations. This approach was based on the concept of Design of Experiments (DOEs) and Response Surface Methodology (RSM). Initially, an extension of Oxleys machining theory incorporating the Johnson-Cook material model was integrated with RSM to accomplish a fast assessment of the material parameters. Having provided the material parameters by Oxleys machining theory, the optimum set of friction coefficients were determined through evaluation of the Finite Element (FE) simulation results. The final step involved direct integration of 2D FE models incorporating the optimum frictional boundary conditions with RSM to reassess the optimum set of material parameters. This approach was implemented to determine the constitutive parameters for wide range of materials including Inconel 718 in aged condition, AISI 1080 plain carbon steel and AA6082-T6 aluminium alloy. The calibration of material models using the presented inverse methodology led to a significant improvement in simulation results. The reasons for the robustness of the proposed inverse methodology were discussed.

Carbon control in PM sintering: industrial applications and experience

Abstract The challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have been proposed to address the problem, these have rarely come to reality and entered industry practice. The purpose of this article is to summarise these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. An important aim is to provide the PM industry with a fresh understanding of furnace operations and to provide recommendations to improve the control of furnace conditions. A case study is given of an existing furnace installation using Sinterflex technology which allows continuous monitoring and/or control of the furnace atmosphere. The reduction of oxides and carbon potentials to optimise the production parameters is described.

XPS study of surface-active organic compounds on fine ferrous powder

Controlled adsorption of organic probe molecules in liquid solutions provides information on the interaction between powder and surface-active additives used in metal injection moulding (MIM). The adsorption of such compounds onto stainless-steel powder and carbonyl iron powder is evaluated by means of XPS. Stearic acid is adsorbed on gas-atomized stainless-steel powder covered mainly by basic manganese oxide. The basic molecule aniline is adsorbed on water-atomized stainless-steel powder having an Si-rich acidic surface oxide. This adsorption takes place preferentially on the silicon oxide. On slightly SiO2-coated carbonyl iron powder, stearic acid as well as aniline are adsorbed. Copyright

Rheological and Thermal Properties of a Model System for PIM

Abstract Powder injection moulding (PIM) is an important and accepted industrial technique for net shaping of precision components which can have a rather complex geometry. In order to meet the imposed, often rather strict, requirements with regard to dimensional accuracy, it is important to have an adequate knowledge and control of the rheological behaviour and the related processing properties of the powder/polymer melt (feedstock). Such a knowledge is furthermore of crucial importance in numerical simulations of the PIM-process. In the present work, a model system, consisting of steel powder, poly(ethylene glycol) and wax, is used in order to illustrate how the viscometric properties as well as thermal properties, such as the conductivity and the specific heat, of the system can be related to the corresponding properties of the polymeric binder system. In a similar way, the pvT (pressure-volume-temperature)-behaviour of the model system is analysed and discussed. The pvT-behaviour, which has not been extensively reported on for PIM-feedstocks, is considered to be of significant relevance for controlling the outcome of the injection moulding process.

Quantitative phase analysis and thickness measurement of surface-oxide layers in metal and alloy powders by the chemical-granular method

The principles of the chemical-granular analysis of metal and alloy powders are reviewed and the results are compared with those provided by the spectroscopic analytical techniques XPS, AES and SIMS, including ion etching in their depth-profiling mode, when they are applied to the same materials. Several examples are analysed and it is shown that the chemical-granular method alone can provide the very same information as depth profiling. However, it is averaged over a macroscopic powder sample in contrast to one or a few single particles. Nevertheless, it is the combination of the chemical-granular and depth-profiling analyses that really provides an unparalleled description in quantitative terms of the phase composition and microstructure of either multiphase and/or irregular surface layers resulting from oxidation, precipitation or contamination.

Wear Evaluation on Ni3Al/MnS Composite Related to Metallurgical Processes

Iron alloyed Ni3Al with composition of Ni-18. 8Al-10. 7Fe-0. 5Mn-0. 5Ti-0. 2B in atom percent (NAC alloy) showed attractive tribological properties under unlubrication condition at room temperature. The alloy was prepared by hot isostatic pressing (HIP) process. The wear properties were associated with its intrinsic deformation mechanism. Unfortunately, the single phase NAC-alloy worked inadequately with its counterpart disk, and also showed a poor machinability. In the present work, NAC-alloy matrix composite with 6% (volume percent) MnS particle addition was studied to improve its wear behaviors and performance on machining. Two metallurgical processes of HIP and vacuum casting were applied to produce the testing materials. Pin-on-disk (POD) measurements were carried out at room temperature. A commercial vermicular graphite cast iron was selected as a reference material. The counterpart disk was made of a grey cast iron as liner material in ship engines. The contact pressures of 2. 83 MPa and 5. 66 MPa were normally applied in the tests. The investigation indicated that MnS particle addition in the NAC-alloy composites functions as an effective solid lubricant, and improved wear properties and machinability of the materials. Obviously, as-cast NAC-alloy with in-situ formed MnS-phase was working more effectively with the counterpart, comparing to the HIPed NAC-alloy composite with MnS particles. At the high contact pressure of 5. 66 MPa, the specific wear rate of the as-cast NAC-alloy composite was high. The phenomenon of the negative effect is mostly due to the brittle second NiAl phase as evidenced in the microstructure analysis.

Effect of silicon, vanadium and nickel on microstructure of liquid phase sintered M3/2 grade high speed steel

Abstract Liquid phase sintering of M3/2 grade high speed steel (HSS) was carried out at 1270°C in high vacuum reaching near full density starting from loose packed powder. Focus is placed on the study of the effects of the addition of Si, Ni and V as elemental powder and cooling rates on the as sintered microstructure, the main objective being improving M6C characteristics and control of pearlite appearance. Slow cooling from the sintering temperature and Si addition in wt% resulted in a completely fine pearlitic matrix with less elongated and more uniformly distributed M6C precipitates. Adding V or Ni in wt-% quantities decreased the amount of pearlite owing to MC formation and delayed pearlite formation. The study involved the use of thermodynamic modelling and sintering cycle optimisation as well as the evaluation of sintered material by means of optical and scanning electron microscopy, X-ray diffraction and hardness testing.

Electron Beam Melting Manufacturing Technology for Individually Manufactured Jaw Prosthesis: A Case Report

In the field of maxillofacial reconstruction, additive manufacturing technologies, specifically electron beam melting (EBM), offer clinicians the potential for patient-customized design of jaw prostheses, which match both load-bearing and esthetic demands. The technique allows an innovative, functional design, combining integrated porous regions for bone ingrowth and secondary biological fixation with solid load-bearing regions ensuring the biomechanical performance. A patient-specific mandibular prosthesis manufactured using EBM was successfully used to reconstruct a patients mandibular defect after en bloc resection. Over a 9-month follow-up period, the patient had no complications. A short operating time, good esthetic outcome, and high level of patient satisfaction as measured by quality-of-life questionnaires-the European Organisation for Research and Treatment of Cancer QLQ-C30 (30-item quality-of-life core questionnaire) and H&N35 (head and neck cancer module)-were reported for this case. Individually planned and designed EBM-produced prostheses may be suggested as a possible future alternative to fibular grafts or other reconstructive methods. However, the role of porosity, the role of geometry, and the optimal combination of solid and porous parts, as well as surface properties in relation to soft tissues, should be carefully evaluated in long-term clinical trials.