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Plasma Surface Engineering by the Numbers
Glow discharges, sheaths, plasma cleaning, plasma nitriding and PVD coatings for tools, dies and machine parts
How low-pressure plasmas clean, nitride and coat steel and carbide parts, and how to specify, run, test and cost plasma nitriding and PVD coatings, worked with numbers.
Start readingAbout this book
A low-pressure plasma is a partly ionised gas, glowing faintly in a steel chamber, in which a small fraction of the atoms have lost an electron. It is a surprisingly practical tool. Ions accelerated across a thin layer at a part’s surface scrub away oxides and oils, heat the part to nitriding temperature, drive nitrogen into its surface, or knock atoms off a metal target so that they condense on the part as a hard coating a few micrometres thick. Plasma nitriding, plasma cleaning and physical vapour deposition (PVD) coatings are now routine on moulds, dies, cutting tools, gears and hydraulic parts, and the people who buy and specify them are rarely plasma physicists.
This book explains what happens inside the chamber, using numbers rather than mysteries. It starts with what a plasma is, how a glow discharge breaks down and sustains itself, and why the sheath at a part’s surface matters most. It then works through plasma cleaning and activation, plasma nitriding and the testing of nitrided layers, sputtering and cathodic arc PVD, coating thickness and uniformity, adhesion and failures, and the economics of treating tools and dies.
It is for manufacturing, tooling, quality and maintenance engineers, toolmakers, heat treaters and buyers. It assumes engineering or trade training and comfort with pressure, temperature, voltage and simple algebra; the physics is explained as it is used. Each chapter works the running case with real numbers, includes one plausible mistake and how it was found, links the BIZOMAT tools that do the chapter’s calculations, and ends with an exercise and its worked answer.
The running case
Every chapter follows one job through one shop. This is an illustration. A surface engineering job shop in Newcastle, New South Wales, treats tools and parts for toolmakers and manufacturers. It has two plasma machines:
- PN-1: a plasma nitriding vessel with a working space 1,000 mm in diameter and 1,600 mm high, a pulsed DC power supply of up to 1,000 V and 60 kW, and gas supplies of nitrogen, hydrogen, argon and methane.
- PV-1: a PVD coater with a chamber about 700 mm across, four chromium magnetron sputtering targets, a pulsed bias supply for the parts and a three-fold planetary rotation fixture.
The job is order 27 from a die-casting toolmaker: 24 core inserts in H13 hot-work tool steel for an aluminium high-pressure die-casting die, each 60 mm in diameter and 150 mm long, hardened and tempered to about 46 HRC. The toolmaker wants a duplex treatment: plasma nitriding to give a hard diffusion zone with no brittle compound layer, followed by a 4 µm chromium nitride (CrN) PVD coating, to reduce soldering of aluminium to the cores and extend their life. The same toolmaker also sends the shop its carbide and high-speed steel cutters for coating.
Masses, settings, temperatures, thicknesses, test results, prices and failure records are the shop’s working figures or are calculated from stated assumptions. They do not describe BIZOMAT work or any real business, equipment maker, coating supplier or customer. Prices are in Australian dollars excluding GST, because a GST-registered business claims the GST back on its costs.
How to use the book
Chapters 1 to 3 explain the plasma, the discharge and the sheath, Chapters 4 to 6 cleaning and nitriding, and Chapters 7 to 10 PVD coatings, their testing and their economics. Read Chapter 1 first; the others stand on their own once the case is familiar. The Library’s Vacuum by the Numbers covers the pumps, leaks and gauges that every plasma machine depends on, and Diffusion by the Numbers the diffusion that sets nitrided case depth.
Each chapter links the BIZOMAT calculators it uses. The tools do the arithmetic; the chapter explains what the inputs mean and where they come from. Every result in the text was checked by calculation, and the numbers in figures match the text.
Limits and responsibility
This book is educational. Plasma machines use high voltages, hydrogen and other flammable or asphyxiant gases, vacuum vessels and high temperatures, and must be designed, installed and operated to the maker’s instructions, the applicable Australian standards and work health and safety law, by trained people. Treatment specifications for real parts must be agreed with the part’s designer and the treater, and verified by test. Standards are named by number and scope only. Process settings, layer depths, hardness values and costs in the case are illustrations; use the equipment maker’s data, the steel maker’s data and your own trials for real work.
Who this book is for
Manufacturing, tooling, quality and maintenance engineers, toolmakers, heat treaters and buyers who specify, run, inspect or pay for plasma nitriding, plasma cleaning and PVD coatings on tools, dies and machine parts.
What you will learn
- Explain what a low-pressure plasma is, how a glow discharge starts and why ions arriving at a part's surface carry the energy that cleans, heats and coats it.
- Plan a plasma cleaning and plasma nitriding cycle, and judge its gas mixture, pressure, power, temperature and time from the numbers.
- Read a nitrided layer's hardness profile and specify its compound layer and diffusion depth for the part's duty.
- Explain how sputtering and cathodic arc PVD deposit coatings, and estimate thickness, rate and uniformity from a coater's settings.
- Test coating thickness and adhesion, find the cause of a failed coating, and work out whether a treatment pays for itself.
Inside this book
Chapters
- 01What a processing plasma isWhat a low-pressure processing plasma is: how few of its atoms are ionised, why its electrons are hot while its gas is not, and how density, Debye length and mean free path describe it.
- 02Breakdown and the glow dischargeHow a gas breaks down into a glow discharge, why the voltage needed depends on pressure times gap, how normal and abnormal glows and arcs differ, and why holes in parts can overheat.
- 03The sheath: where ions gain their energyWhy a charged sheath forms where a plasma meets a surface, how fast ions enter it, how thick it is, what energy ions arrive with, and how a Langmuir probe measures the plasma.
- 04Plasma cleaning and activationWhat plasma can and cannot clean, how sputter etching and hydrogen remove oxides and how fast, how plasma activates plastics, and why wet precleaning still decides the result.
- 05Plasma nitriding: gas, heat and timeHow plasma nitriding hardens steel, how the gas mixture controls the compound layer, what gas flows and power a load needs, and how case depth grows with time.
- 06Testing a nitrided layerHow to prove a nitrided layer with coupons, metallography and a microhardness traverse, how to read nitriding depth, and why a Rockwell C test on a nitrided surface misleads.
- 07PVD coatings by sputtering and arcHow magnetron sputtering and cathodic arc deposit hard nitride coatings, why crossed fields trap electrons, how fast metal is sputtered, and how reactive gas and bias shape the film.
- 08Coating thickness, uniformity and measurementWhy PVD coating thickness varies with line of sight, rotation, distance and loading, how to measure it with the ball crater test, and how to judge a coating process's capability from witness coupons.
- 09Adhesion, hardness and coating failuresWhat makes a PVD coating stick, how indentation and scratch tests judge adhesion, why measuring a thin coating's hardness needs very small loads, and how to trace a coating failure back to its cause.
- 10What plasma treatments are worthHow to judge whether nitriding and PVD coatings pay: cost per thousand shots for die tooling, Taylor tool life for coated cutters, and a treater's business case for a coater.
Apply This in Practice
Use these BIZOMAT tools to try the method from this reading with your own numbers.
Applies this method
Equipment Investment Appraisal (NPV, IRR, Payback, B/C, EUAC)
Appraises a surface treatment shop's purchase of a PVD coater from its price, coating income and running costs: NPV, IRR and payback over ten years.
Used in What plasma treatments are worth
Applies this method
Gas Mixture Properties (Dalton: Molar Mass, Gas Constant, Specific Heats, Density, Partial Pressures, Mixing Entropy)
Gives the molar mass, density and partial pressures of argon–hydrogen and nitrogen–hydrogen mixtures used for plasma cleaning and nitriding at chamber pressure.
Used in Plasma cleaning and activation
Applies this method
Gas Volume at Pressure and Temperature
Converts a nitriding vessel's standard gas flows to the actual volume flow at 300 Pa and 520 °C, from which the gas residence time in the chamber follows.
Applies this method
Pressure and Stress Converter
Converts plasma nitriding and sputtering pressures between pascals, millibar and torr, the mixed units found on plasma machines, gauges and coating data sheets.
Used in What a processing plasma is
Applies this method
Process Capability Check (σ from R̄, Cp, Cpk, Rejects, Limits)
Judges PVD coating thickness capability from ball-crater readings on witness coupons and on parts, giving the process sigma, control limits, Cp and Cpk.
Applies this method
Taylor Tool Life and Economic Cutting Speed
Fits Taylor tool life to uncoated and PVD-coated end mill tests and compares their minimum-cost and maximum-production cutting speeds.
Used in What plasma treatments are worth
Applies this method
Vickers and Knoop Hardness from Indentation
Turns indentation diagonals from a nitrided layer's microhardness traverse into Vickers or Knoop hardness and checks the indentation depth against the layer thickness.
Used in Testing a nitrided layer
References and source notes
The manuscript and worked examples are original BIZOMAT writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 2 November 2026.
- P. M. Bellan, Cambridge University Press. Fundamentals of Plasma Physics (2006). Copyright work, used only as a map of ideas: plasma parameters, Debye shielding and quasi-neutrality, collisions with neutrals, sheaths and Langmuir probes, and the drift of charged particles in crossed electric and magnetic fields. The copy consulted was a 2004 manuscript of the book. No text, equations as set out there, figures or problems are reproduced, and all cases and calculations are BIZOMAT originals.
- M. A. Lieberman and A. J. Lichtenberg, Wiley. Principles of Plasma Discharges and Materials Processing, second edition (2005). Background for glow discharges, the Bohm criterion, collisionless and collisional sheaths, sputtering and plasma processing in Chapters 1 to 4 and 7.
- B. Chapman, Wiley. Glow Discharge Processes: Sputtering and Plasma Etching (1980). Background for the structure of the glow discharge, breakdown, the hollow cathode effect and sputtering in Chapters 2, 4 and 7.
- D. M. Mattox, William Andrew. Handbook of Physical Vapor Deposition (PVD) Processing, second edition (2010). Background for substrate preparation, sputter and arc deposition, film growth, thickness and adhesion testing in Chapters 4 and 7 to 9.
- E. J. Mittemeijer and M. A. J. Somers (editors), Woodhead Publishing. Thermochemical Surface Engineering of Steels (2015). Background for the compound layer and diffusion zone of nitrided steels, nitriding potential and case growth in Chapters 5 and 6.
- F. Paschen, Annalen der Physik 273(5), 69–96. Ueber die zum Funkenübergang in Luft, Wasserstoff und Kohlensäure bei verschiedenen Drucken erforderliche Potentialdifferenz (1889). Named in Chapter 2 as the original measurements of breakdown voltage against pressure and gap that give the Paschen curve.