Hard Chrome Electroplating via Pulsed Current and Negative Pressure
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Solution Overview
Problem
Existing methods for depositing hard chrome layers on substrates face issues with internal tensile stresses leading to cracks and corrosion, and high deposition rates are hindered by hydrogen formation and porosity, which compromise both corrosion resistance and mechanical properties.
Innovation Solution
A galvanic deposition method involving a gas-tight container with negative pressure and relative movement between the substrate and electrolyte, using a combination of pulsed and direct currents, and a pressure difference to minimize hydrogen bubble formation and deposit a layer with reduced internal stresses and microcracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher current densities are used to achieve high deposition rates, then productivity is improved, but hydrogen bubbles form on the substrate surface causing pores and defects that worsen reliability
Solution Approach 1:
The patent applies pulsed current instead of continuous current during galvanic deposition. The current is periodically switched on and off, allowing hydrogen bubbles to detach during the off-periods while chromium deposition continues during on-periods. This periodic action prevents bubble accumulation and pore formation, enabling high deposition rates without compromising layer quality
Solution Approach 2:
The patent introduces dynamic movement between the substrate and electrolyte during deposition. The substrate surface and electrolyte are moved relative to each other at speeds of 0.1-5.0 m/s, creating dynamic conditions that prevent hydrogen bubble adhesion and promote uniform chromium deposition, thereby maintaining reliability at high productivity
2Ease of manufacture
If conventional galvanic deposition is used, then manufacturing simplicity is maintained, but internal tensile stresses cause cracks and corrosion that worsen reliability
Solution Approach 1:
The pulsed current application creates periodic deposition cycles that allow stress relaxation between pulses. This periodic action reduces the accumulation of internal tensile stresses that would otherwise lead to microcracks and corrosion, improving reliability while maintaining process simplicity
Solution Approach 2:
The relative movement between substrate and electrolyte introduces a dynamic element that prevents stagnant conditions and uniform stress distribution. This dynamic interaction helps reduce internal tensile stresses and prevents crack formation, thereby improving reliability without significantly complicating the manufacturing process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves high deposition rates with hard chrome layers that are essentially pore-free, offering enhanced corrosion resistance and mechanical properties, including improved tribological performance.
Implementation Method 1
For the galvanic deposition of chromium layers, the substrate surfaces to be coated are brought into contact with an electrolyte containing at least the metal to be deposited (chromium) after a suitable pretreatment for preparing the surface, with a deposition voltage being applied between the cathodic contacted substrate surface and an anode. As a result, the chromium dissolved in the electrolyte is deposited as a layer on the substrate surface.
Implementation Method 2
In addition, it is suspected that the unavoidable occurrence of gaseous H2 during the deposition of Ab chromium layers leads to the incorporation of hydrogen into the layer and the substrate, which in turn can lead to the formation of cracks in the layer and damage to the substrate.
Implementation Method 3
wherein at least during the application of the voltage in the container that is essentially gas-tight with respect to the environment a negative pressure is set
Implementation Method 4
the substrate surface and chromium-containing electrolyte are moved at a relative speed of > 1 m/s to 5 m/s to one another
Implementation Method 5
a pulse voltage with a frequency of 5 Hz to 5000 Hz, preferably between 50 Hz and 1000 Hz, is applied to deposit the first hard chrome layer
Data Source
AI summary
The method comprises contacting a substrate surface to be coated with chromium-containing electrolytes in a cell at 30-85[deg] C for galvanic deposition, and applying a voltage between the substrate surface to be coated and a counter electrode for galvanically depositing a first hard chromium layer on the substrate surface, where the deposition takes place in a container that is gas-tight against environment and a low pressure is adjusted during applying the voltage in the container. The substrate surface and chromium-containing electrolytes are moved with relative speed of greater than 1-5 m/s. The method comprises contacting a substrate surface to be coated with chromium-containing electrolytes in a cell at 30-85[deg] C for galvanic deposition, and applying a voltage between the substrate surface to be coated and a counter electrode for galvanic deposition of a first hard chromium layer on the substrate surface, where the deposition takes place in a container that is gas-tight against the environment and a low pressure is adjusted during applying the voltage in the container. The substrate surface and chromium-containing electrolytes are moved with a relative speed of greater than 1-5 m/s. A second hard chromium layer is deposited on the first hard chromium layer, where a pulse current is applied between the substrate surface and the counter electrode for the deposition of the first hard chromium layer and a direct current is applied for the deposition of the first hard chromium layer on the second hard chromium layer. A pressure difference is adjusted to an ambient pressure of 20-200 mbar. The pulse current for the deposition of the first hard chromium layer is applied with a frequency of 50-1000 Hz. For the deposition of the hard chromium layer, a current density is adjusted to 50-500 A/dm 2>, where pH value in the electrolytes is adjusted to = 1. The chromium-containing electrolytes flow into the cell from below and over an overflow.