The influence of nickel additions on powder metallurgy gear tooth root strength

November 30, 2011

Gear applications have emerged as an important target for the PM structural parts sector and several of the leading PM groups have developed new processing methods, such as overall or selective densification of sintered preforms, in order to attack this market opportunity.

However, not all potential PM gear applications require these densification processes and it is important to be able to analyse the requirements of various applications in order to optimise the choice of material and processing sequence and therefore deliver the required performance at minimum cost.

As a contributor to a programme with this overall objective, the influence of nickel additions to a sintered hardened Fe-1.5%Mo-0.6%C base material on tooth bend fatigue strength has been studied in a paper reported by A DeNicolo (GKN Sinter Metals, Brunico, Italy) and D Rubesa (University of Applied Science Joanneum, Graz, Austria) at the Euro PM 2011 Conference, held in Barcelona, 9-12 October, 2011. Dr David Whittaker reports exclusively for

Development of Specific Design Criteria for the Optimization of Sintered Gears: The Influence of Nickel on Tooth Root Strength

In this study, three different powder mixtures were processed (Table 1). These compositions were based on Fe-1.5%Mo-0.6%C, to which were added 2% Cu (DDH2),  2%Ni (DDC2) or 2%Cu + 4%Ni (DHP2). As a result of these additions, the amounts of Fe-Ni austenite in the final microstructure varied.


Table 1 Chemical compositions of the materials investigated (wt%)*    


Fig. 1 The test gear*  

Gear components, as shown in Fig. 1 and defined in terms of design parameters in Table 2, were cold compacted from each of these powder mixtures and the compacts were sinter hardened in a belt furnace at 1120°C in endogas and tempered in air at 180oC. In all cases, the sintered density level was 7.0 g/cm3. The carbon potential of the sintering atmosphere was set at 0.65%C.

The sintered hardened microstructures created with these three powder mixtures are shown in Figs. 2 In all materials, the predominant microstructural phase was martensite, but the amount of Fe-Ni austenite increased as the nickel level in the powder increased.


Table 2 Design parameters of the test gear*


Fig. 2 Microstructures created with these three powder mixtures*


Table 3 Microhardness determinations for the three sinter hardened structures* 


Fig. 3 Mounting of the gear during pulsator rig testing*

Microhardness determinations were made in the martensite and austenite phases in each material (Table 3). The slightly higher hardness levels in material DDC2 was related to the higher carbon content (0.65% vs 0.6%) in this material.

Tooth root bend fatigue tests on the sinter hardened parts were carried out on a custom-made pulsator test bench (Fig. 3).


Fig. 4 Calculation of the survival probability at 3500 N load*

Test results at each load level were presented as number of cycles vs. probability of survival, calculated using the Weibull and Gassner method. An example of such a plot is shown in Fig. 4.

From this type of plot, the loads for probabilities of survival of 10% and 90% were calculated and finally these loads were converted into stresses using a calculation model based on DIN 3990 Part 3.


Fig. 5 Calculation model of the analysed gear (a) and von Mises stress in the tooth root and the corresponding sub-model (b)*

To verify the results, a finite element analysis was carried out. In this analysis, the gear was loaded in the same manner as in the tests on the pulsator rig (Fig. 5a). At a given load, the maximum von Mises stress in the tooth root was calculated (Fig. 5b). The small differences between the two types of calculation can be seen in Table 4, confirming the validity of the chosen calculation method for the evaluation of the test results.


Table 4 Comparison of calculated tooth root endurance limits for each material with the FEA results*

A general trend in these results could be recognised. As nickel content increased, the proportion of Fe-Ni austenite in the microstructure increased and this increase in the proportion of the softer phase could be linked to a reduction in fatigue strength.


* Images from the paper by A DeNicolo et al, ‘Development of Specific Design Criteria for the Optimization of Sintered Gears: The Influence of Nickel on Tooth Root Strength’ presented at Euro PM2011 Conference. Published in the Conference Proceedings by EPMA, UK)   


Author: Dr David Whittaker is a consultant to the Powder Metallurgy and associated industries. Contact +44 1902 338498 email: [email protected]  


News | Articles | Market reviews | Search directory | Subscribe to e-newsletter

November 30, 2011

In the latest issue of PM Review…

Download PDF

Extensive Powder Metallurgy industry news coverage, and the following exclusive deep-dive articles and reports:

  • From powder modification to rejuvenation: Fluidised Bed Reactors in metal powder production and Additive Manufacturing
  • Retech: Enabling the atomisation of reactive and refractory alloys at substantially higher levels of productivity and lower cost
  • Sustainability in Powder Metallurgy: Highlights from the 41st Hagen Symposium
  • Innovations from Japan’s Powder Metallurgy industry: award winners highlight novel automotive and healthcare applications

The latest news from the world of metal powders, delivered to your inbox

Don't miss any new issue of PM Review, and get the latest industry news. Sign up to our weekly newsletter.

Sign up

Join our community

Discover our magazine archive…

The free-to-access PM Review magazine archive offers unparalleled insight into the world of Powder Metallurgy from a commercial and technological perspective through:

  • Reports on visits to leading PM part manufacturers, metal powder manufacturers and industry suppliers
  • Articles on technology and application trends
  • Information on materials developments
  • Reviews of key technical presentations from the international conference circuit
  • International industry news

All past issues are available to download as free PDFs or view in your browser.


Browse the archive


Looking for PM production equipment, metal powders, R&D support and more?

Discover suppliers of these and more in our
advertisers’ index and buyer’s guide, available in the back of PM Review magazine.

  • Powders & materials
  • Powder process, classification & analysis
  • PM products
  • Atomisers & powder production technology
  • Compaction presses, tooling & ancillaries
  • Sintering equipment & ancillaries
  • Post-processing
  • Consulting & toll sintering
View online
Share via
Copy link