Case StudyAmorphous carbon on M2 steel

The harder coating was not the more durable coating.

Nine depositions looked like a recipe-tuning problem. Together, they exposed a material constraint: the energy that hardened a-C also reduced thickness and adhesion.

The engineering question

Can one a-C layer deliver thickness, hardness and adhesion?

Evidence available

Nine comparable a-C depositions spanning two bias regimes, gas-flow and pulse settings.

How Theorema Coatings solved it
  1. 01
    Reconstructed the process

    Converted ion-probe traces into surface ion energy.

  2. 02
    Calculated the relationships

    Calculated how hardness, thickness, stress and adhesion changed across all nine runs.

  3. 03
    Challenged the explanation

    Tested the stress–thickness model and 0.15 GPa rule against observed peeling.

  4. 04
    Turned evidence into a decision

    Separated measured, interpreted and proposed evidence; the result pointed to a layered coating.

What the panel revealed

Higher ion energy increased hardness while thickness and adhesion fell. Residual stress alone did not distinguish held coatings from peeled ones.

Stress and adhesion by reconstructed ion energy Three held coatings occupy the lower-energy regime and six peeled coatings the higher. Three peeled below 0.15 gigapascal show that stress alone cannot screen adhesion. LOW-BIAS REGION HIGH-BIAS REGION 0.050.100.150.200.25 0.15 GPa reference residual stress (GPa) 3 peeled films below the stress reference ~50 eV / 80 V · 3 held~85 eV / 150 V · 6 peeled
Recorded outcome, not a universal threshold. Ion energy follows the report’s probe reconstruction; each condition appeared once.
  1. 01

    Hardness came with a cost

    Across nine runs, hardness reached 13.6 GPa as thickness and adhesion fell (r = −0.93 and −0.88).

  2. 02

    The stress screen missed failures

    Three of six peeled coatings were below 0.15 GPa. Stress alone would have passed failed films.

  3. 03

    One layer carried three jobs

    One deposition-energy setting controlled all three properties. No tested recipe met every target.

Recommendation

Separate the three jobs across a graded coating.

A single a-C film could not deliver all three outcomes. Assign adhesion, thickness and hardness to separate layers.

Best measured single-layer results

CandidateBiasAr flowThicknessHardnessStressLc2 / Lc3Wear
Stress / Lc2 margin80 V120 sccm1190 nm7.1 GPa0.077 GPa43 / 59 N168
Wear / Lc380 V90 sccm1200 nm7.8 GPa0.133 GPa25 / 62 N79