Complex metal structure with glowing blue energy, representing controlled stress during laser deposition.

Decoding Cracks: How Deposition Techniques Impact the Strength of Metal Alloys

Lena Voss in Tech & Innovation September 2025 • 4 min read.

"Dive into the science of metal deposition and discover how controlling the process can prevent structural failures."

In the world of aerospace, where precision and reliability are paramount, the nickel-based IN718 superalloy stands as a critical material. Known for its exceptional strength at high temperatures, its resistance to corrosion, and its impressive fatigue strength, IN718 is a staple in the construction of aero engine components. However, these components, particularly turbine blades, face constant stress and vibration, making them susceptible to fatigue and potential failure.

To combat this, laser additive manufacturing has emerged as a key technique for repairing damaged components and creating new ones. This method involves depositing materials layer by layer using a high-energy beam, allowing for precise control over the final product. Yet, the very process that makes it so valuable—the rapid heating and cooling—can also introduce significant residual stress, leading to hot cracking in the deposited alloy. Overcoming this cracking is essential to ensure the integrity and longevity of these critical parts.

Recent research has focused on understanding and mitigating weld metal liquation cracking, a common issue in laser-deposited IN718 alloys. While some micro-cracks can heal, larger issues like pores, coarse eutectic formations, and thermal stress remain a concern. This article will delve into a study analyzing how different alloying powders and cooling conditions affect crack formation in laser-deposited IN718 alloys. We'll explore the microstructural characteristics and analyze the impact of metallurgical factors and residual stress on crack sensitivity.

How Do Deposition Parameters Influence Crack Sensitivity?

Complex metal structure with glowing blue energy, representing controlled stress during laser deposition.

A study examined the effects of varying deposition parameters on the microstructure and crack susceptibility of IN718 alloys. Researchers fabricated IN718 alloys using laser cladding under different conditions, carefully analyzing the resulting microstructures and crack formations. This meticulous approach allowed them to pinpoint the factors that contribute to cracking and identify potential strategies for improvement.

The investigation revealed several key insights into the cracking behavior of laser-deposited IN718 alloys. One significant finding was the presence of continuous dendritic Laves phases, which formed an interface with the austenite matrix. This interface exhibited an uneven distribution of nanohardness, indicating variations in the material's resistance to deformation at a very small scale. The weld metal liquation cracking tended to spread along both the laser scanning direction and the buildup direction, suggesting a complex interplay of forces at work during crack propagation.

Dendritic Laves Phases: Continuous formations create weak interfaces susceptible to cracking.
Nanohardness Distribution: Uneven hardness indicates stress concentrations, promoting crack initiation.
Crack Propagation: Cracks spread along laser scanning and buildup directions, influenced by residual stress.

Furthermore, the research highlighted the role of Nb/Mo-enriched granular clusters on the crack surface, suggesting that these elements play a crucial role in the cracking mechanism. The amount of coarse eutectic phases, which appear as dendrites or networks, increased when using composite IN718/C-Fe-Cr powder and a slow cooling rate. Faster cooling rates reduced both the total crack length and maximum crack length. Interestingly, increasing the number of buildup layers led to higher transverse residual stress, suggesting that the deposition process itself contributes to the problem.

Engineering Stronger Alloys for the Future

This research provides valuable insights for optimizing laser deposition processes to minimize cracking in IN718 alloys. By carefully controlling cooling rates, alloy composition, and deposition parameters, manufacturers can reduce the risk of crack initiation and propagation, leading to stronger, more reliable components. The findings emphasize the importance of understanding the complex interplay between metallurgical factors and residual stress in additive manufacturing, paving the way for improved techniques and more durable materials in aerospace and other critical industries.

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This article is based on research published under:

DOI-LINK: 10.1007/s11665-017-2966-2, Alternate LINK

Title: Sensitivity Of Liquation Cracking To Deposition Parameters And Residual Stresses In Laser Deposited In718 Alloy

Subject: Mechanical Engineering

Journal: Journal of Materials Engineering and Performance

Publisher: Springer Science and Business Media LLC

Authors: Yaocheng Zhang, Li Yang, Tingyi Chen, Song Pang, Weihui Zhang

Published: 2017-10-03

Everything You Need To Know

What are the primary challenges associated with using laser additive manufacturing for IN718 alloys, and why is it important to address them?

Laser additive manufacturing of IN718 alloys involves depositing material layer by layer using a high-energy beam. Rapid heating and cooling during this process can introduce residual stress, leading to hot cracking. Overcoming this cracking is essential for ensuring the integrity and longevity of critical components. This is often addressed through careful control of deposition parameters like cooling rates and alloy composition. The research highlights the importance of understanding the complex interplay between metallurgical factors and residual stress in additive manufacturing. Further research is needed to optimize these deposition techniques.

How do specific deposition parameters, such as cooling rates, impact the crack sensitivity of laser-deposited IN718 alloys?

Deposition parameters influence crack sensitivity in IN718 alloys through their effects on microstructure and residual stress. For instance, slower cooling rates can increase the amount of coarse eutectic phases, promoting crack formation. The formation of continuous dendritic Laves phases creates weak interfaces susceptible to cracking. Uneven nanohardness distribution indicates stress concentrations, which can promote crack initiation. Controlling these parameters is key to minimizing cracking.

What role do dendritic Laves phases play in the cracking behavior of laser-deposited IN718 alloys?

The study found that continuous dendritic Laves phases, forming an interface with the austenite matrix, contribute to cracking in IN718 alloys. These phases create weak interfaces susceptible to crack propagation. Additionally, the distribution of nanohardness along this interface is uneven, suggesting stress concentrations that promote crack initiation. The presence of Nb/Mo-enriched granular clusters on the crack surface also indicates their role in the cracking mechanism.

In what directions does weld metal liquation cracking tend to spread in laser-deposited IN718 alloys, and what does this indicate about the cracking mechanism?

Weld metal liquation cracking in laser-deposited IN718 alloys spreads along both the laser scanning direction and the buildup direction. This suggests a complex interplay of forces at work during crack propagation. The orientation of the laser scan relative to the growth direction will impact crack formation. This emphasizes the need for controlling the deposition parameters to minimize the residual stress and mitigate the risk of cracking.

According to the research, how can laser deposition processes be optimized to minimize cracking in IN718 alloys?

Optimizing the laser deposition processes can minimize cracking in IN718 alloys by carefully controlling cooling rates, alloy composition, and deposition parameters. The research emphasizes understanding the interplay between metallurgical factors and residual stress in additive manufacturing. Composite IN718/C-Fe-Cr powder and slower cooling rates, for example, increase the amount of coarse eutectic phases, promoting crack formation. Faster cooling rates reduce both the total crack length and maximum crack length.