R. Haubner, E. Rauchenwald, M. Lessiak, R. Pitonak and R. Weissenbacher
Investigations of hard and wear resistant materials have a long tradition to increase the performance and profitability of machining applications. The evolution started with WC-Co hardmetal alloys, which were produced by PM technology, followed by CVD coatings on hardmetal tools. The first CVD coatings applied were TiC, TiN and Al2O3. The properties of these coatings could be optimized by varying the crystal size, crystal orientation but also combination of the materials in multilayer systems. Nowadays, about 85% of all hardmetal tools are coated.During the last years, driven by PVD coatings showing good performance (e.g. TiAlN), the search for new CVD coatings was intensified. Medium temperature (MT) CVD processes for TiCN allowed the deposition of TiCN crystals with different composition side by side. Due to this microstructure the adhesion between single layers in new multilayer coatings like TiN/MT-TiCN/Al2O3/TiN could be increased. Novel (Ti,Al)N coatings were developed, showing a nanolamellae microstructure consisting of self-assembled (Ti,Al)N with different composition.
For the future there is still plenty to investigate. The already existing coatings and coating systems have to be optimized for the various machining applications. To find new types of CVD coatings, we look for chemical reactions practicable for its use in CVD equipment.
M. Vattur Sundaram, R. Shvab, S. Millot, E. Hryha and L. Nyborg
In order to be cost effective and to meet increasing performance demands, powder metallurgy steel components require continuous improvement in terms of materials and process development. This study demonstrates the feasibility of manufacturing structural components using two different alloys systems, i.e. lean Cr-prealloyed and diffusion bonded water atomised powders with different processing conditions. The components were sintered at two different temperatures, i.e. 1120 and 1250 °C for 30 minutes in three different atmospheres: vacuum, N2- 10%H2 atmosphere as well as lean N2-5%H2-0.5%CO-(0.1-0.4)%CH4 sintering atmosphere. Components after sintering were further processed by either low pressure carburizing, sinterhardening or case hardening. All trials were performed in the industrial furnaces to simulate the actual production of the components. Microstructure, fractography, apparent and micro hardness analyses were performed close to the surface and in the middle of the sample to characterize the degree of sintering (temperature and atmosphere) and the effect of heat treatment. In all cases, components possess mostly martensitic microstructure with a few bainitic regions. The fracture surface shows well developed sinter necks. Inter- and trans-granular ductile and cleavage fracture modes are dominant and their fraction is determined by the alloy and processing route.
R. Shvab, M. V. Sundaram, H. Karlsson, D. Chasoglou, S. Berg, E. Hryha and L. Nyborg
Increasing the application area of powder metallurgy (PM) steels for manufacturing of high-performance structural components results in material saving, reduction in energy consumption, etc. In this study, feasibility of the manufacturing of valve bridge component for heavy duty engine utilizing lean alloyed powders and novel vacuum sintering approach, followed by low pressure carburizing, is studied. Three low alloyed steel powders were processed by conventional uniaxial pressing and sintering at 1120 and 1250°C in industrial vacuum furnace. The components were tested under high cycle fatigue testing, simulating real conditions of operation. Fatigue properties did not show significant dependence on the sintering temperature and were comparable to currently used reference cast material. Fracture surfaces of broken samples were analyzed to detect crack initiations and fracture mechanisms as well as quality of sintering. Results showed preferentially ductile failure, well developed sintering necks and clean pore surfaces, indicating good sintering. Tested material in combination with novel vacuum sintering process show to be an attractive alternative for manufacturing of this type of components for heavy duty engine applications.
Raquel de Oro Calderon, Maryam Jaliliziyaeian, John Dunkley, Christian Gierl-Mayer and Herbert Danninger
The Masteralloy (MA) alloying route has a great potential for reducing the alloying costs in sintered steels, while allowing the introduction of innovative alloying systems. However, in order to achieve an efficient use of the alloying elements, the particle sizes needed are often below 25 µm, which means that for standard gas atomization a significant fraction of the batch has to be discarded or at least recycled. This work evaluates the performance of steels containing MA powders obtained with a novel atomization technique (Ultra-High-Pressure Water atomization) that allows the production of low-cost powders with low oxygen contents, rounded morphologies and mean particle sizes as low as 6 microns. Mechanical properties, dimensional variations and interstitial contents were measured in steels containing different MA compositions sintered at either 1120 °C or1250 ºC in N2-5H2 atmospheres. Already with less than 3 wt.% of alloying elements these steels present excellent combinations of properties, reaching strength levels of 560-915 MPa and hardness 220-260 HV10, combined with elongations of 1.3-3.2% and impact energies around 20-30 J/cm2.
Refurbishment of worn Dies is an interesting research area which also has high economic benefit. Material which is used in PM dies for compacting powders are high carbon steel which have very low weldabilitis. Due to the high hardness, high carbon content and martensitic microstructure, these Dies are very sensitive to the thermal shock produced from fusion welding. For successfully refurbishing the worn Dies, Fine spark deposition was used for deposition of a new layer on the cold work 1.2436 steel. Different heat inputs were used for deposition of nickel based material and finally microstructure and HAZ were studied. Results show the HAZ area is very narrow, free from cracks and HAZ microstructure is similar to the base metal. GTAW welding using same filler metal induced many cracks in HAZ of weld which is detrimental to the refurbished Die performance. Results show increasing heat input in Fine spark deposition can results in crack formation in HAZ even if the weld pool does not occurred in base metal. However these cracks are much smaller than those occurred in GTAW.
 Daninger, H., Pöttschacher, R., Bradac, S., Šalak, A., Seyrkammer, J.: Powder Metallurgy, vol. 48, 2005, no. 1, p. 23
 Pavlina, EJ., Van Tyne, CJ.: Journal of Materials Engineering and Performance, vol. 17, 2008, no. 6, p. 888
 MPIF Standard 35 2016 edition, 2016, p. 1–102
 Dudrová, E., Kabátová, M. In: Fractography of Sintered Materials Principles and Application – Workshop, 2015, p. 227