Nitrogen-Alloyed Overlay Alloy Reciprocating Friction and Wear Behavior

Literature Overview

This study published in Tribology Transactions (2020, Vol. 40, No. 5) by researchers from Hohai University investigates the reciprocating friction and wear performance of nitrogen-alloyed overlay alloys deposited on martensitic stainless steel substrates. The work is supported by the National Natural Science Foundation of China and addresses a practical engineering challenge: improving tribological performance of overlay coatings under cyclic loading conditions through nitrogen incorporation and nitrogen-fixation elements (Nb, Ti).

Core Technical Content

The research introduces nitrogen into martensitic stainless steel overlay alloys using niobium and titanium as nitrogen-fixation elements to form carbonitrides. Reciprocating friction and wear tests were conducted at three load levels (5 N, 10 N, and 15 N) to compare nitrogen-added and non-nitrogen-added overlay alloys.

Key Findings

Parameter	Non-Nitrogen Alloy	Nitrogen-Alloyed Alloy
Primary wear mechanisms	Abrasive + surface fatigue	Abrasive + surface fatigue (improved)
Carbonitride distribution	Sparse, coarse	Dispersed along martensite matrix and grain boundaries
Surface cutting marks	More numerous, deeper	Fewer, shallower
Fatigue spalling	Severe	Significantly improved
Strengthening mechanism	Limited	Grain refinement + dispersion strengthening

The carbonitrides formed by nitrogen fixation elements precipitate dispersely along the martensite matrix and grain boundaries, providing both grain refinement strengthening and dispersion strengthening effects. These mechanisms enhance the matrix resistance to plastic deformation and improve the ability to resist abrasive wear.

Wear Mechanism Analysis

The reciprocating friction process subjects the overlay surface to periodic loading, resulting in pronounced cutting marks and plastic deformation on the friction surface. The dominant wear mechanisms are abrasive wear and surface fatigue wear. The nitrogen-alloyed variant demonstrates superior performance because:

Carbonitrides act as hard second-phase particles that impede dislocation motion during sliding
Grain boundary precipitation impedes crack initiation and propagation
Improved fatigue spalling resistance reduces material loss under cyclic contact stress
The combined strengthening mechanisms increase the hardness gradient across the overlay depth

Engineering Practice Implications

For piping and fitting applications where overlay coatings are used in reciprocating motion environments (such as pump sleeves, valve stems, and reciprocating compressor components), this research suggests that nitrogen alloying with Nb and Ti can significantly extend service life. The key process parameters to control include:

Nitrogen partial pressure during welding to ensure adequate nitrogen pickup
Nb and Ti content to maximize nitrogen fixation efficiency
Cooling rate to promote fine carbonitride precipitation
Heat input to avoid excessive grain growth in the overlay

Study Insights and Reflections

The study demonstrates a clear correlation between microstructural refinement and tribological performance improvement. The fact that carbonitrides preferentially distribute along grain boundaries is particularly significant for fatigue wear resistance, as grain boundaries are typical crack initiation sites. From a practical standpoint, the load-dependent wear behavior indicates that nitrogen alloying provides the most benefit under higher contact stresses (15 N condition), which aligns with heavy-duty industrial applications. Engineers designing overlay coatings for reciprocating components should consider nitrogen alloying as a viable strategy, particularly when combined with appropriate Nb and Ti additions to ensure stable carbonitride formation. The work provides a solid foundation for further optimization of nitrogen content and alloying element combinations to tailor tribological properties for specific service conditions.