In the rapidly evolving field of additive manufacturing (AM), Titomic’s Kinetic Fusion™ (TKF) stands out as a pioneering solid-state process that leverages cold spray technology to build large-scale metal parts and coatings. Unlike traditional melt-based methods such as laser powder bed fusion or directed energy deposition, TKF accelerates metal particles at supersonic speeds without melting them, relying on kinetic energy for bonding. This approach minimizes thermal distortions, enables multi-material deposition, and supports high deposition rates, making it ideal for industries like aerospace, defense, and oil & gas.
As of November 2025, Titomic has made significant strides, including strategic partnerships and expansions that underscore its growing impact. For instance, the company announced a collaboration with Northrop Grumman to revolutionize high-performance pressure vessel manufacturing using TKF, aiming for enhanced strength and sustainability. Additionally, Titomic established a supply and development partnership with Amaero for aerospace and defense applications, and opened a new 59,000 sq. ft. global headquarters in Huntsville, Alabama, to drive U.S. expansion. These developments build on TKF’s foundation in cold spray additive manufacturing (CSAM), a technique with roots in coating technologies but now scaled for full part production.
In this detailed scientific blog, we’ll dissect the TKF process, delve into the underlying bonding mechanisms at the micro- and nano-scales, explore Titomic’s applications and recent innovations, and discuss implications for advanced materials research. Drawing from established literature and recent 2025 reviews, this overview highlights how TKF bridges physics, metallurgy, and nanotechnology.
Process Overview: How Kinetic Fusion Works
TKF is a form of CSAM where metal powders are propelled at high velocities to form deposits without liquefaction. The process avoids the pitfalls of melt-based AM, such as phase transformations, oxidation, and residual stresses from cooling.
Here’s a step-by-step breakdown:
- Feedstock Preparation: Metal powders, such as titanium, titanium alloys, steel, copper, nickel, or magnesium, are selected. TKF is compatible with a wide range of materials, including thermally sensitive alloys and composites. Recent partnerships, like with Metal Powder Works, integrate advanced powder production technologies to optimize feedstock morphology and consistency.
- Particle Acceleration: Powders are injected into a high-pressure gas stream (typically nitrogen, helium, or argon mixtures) heated to enhance particle velocity but kept below melting points. The gas expands through a de Laval nozzle, achieving supersonic speeds (300–1200 m/s). Particle dynamics, including velocity and temperature, are critical for deposition efficiency.
- Impact and Deposition: Particles strike the substrate or prior layers, converting kinetic energy into plastic deformation and localized heating. Bonding occurs above a material-specific critical velocity (V_crit), leading to layer buildup.
- Build-Up and Finishing: Repeated passes create near-net-shape parts. TKF’s large build envelope—up to 9 m × 3 m × 1.5 m—supports massive components, with deposition rates reaching 20–45 kg/h. Post-processing, like heat treatment, may enhance properties.
A key advantage is the solid-state nature, enabling hybrid materials and repairs without thermal damage. For visualization, consider this schematic of the cold spray process:
Recent advancements include Titomic’s new XYZ Plotter and proprietary software for enhanced precision in cold spray manufacturing. This tool improves geometrical control, addressing challenges in deposit shape prediction.
Bonding Mechanisms: A Micro- and Nano-Scale Perspective
The core of TKF’s efficacy lies in its bonding mechanisms, which remain a focal point of research. Recent 2025 reviews emphasize multi-faceted processes involving mechanical, metallurgical, and dynamic phenomena. Unlike melt-based AM, bonding occurs without fusion, preserving feedstock properties.
Critical Velocity and Energy Dynamics
Bonding requires particles to exceed V_crit, typically 300–1200 m/s, depending on material, size, and conditions. The kinetic energy equation is fundamental:
where ( m ) is particle mass and ( v ) is velocity. Above V_crit, energy converts to plastic deformation, adiabatic heating, and interface disruption. Below it, particles rebound. Factors like oxide thickness increase V_crit, as thicker layers demand more energy for fracture.
Impact Deformation and Adiabatic Shear Instability (ASI)
Upon impact, high strain rates 
Local temperature rise in shear bands can be approximated as:
where 
Oxide Disruption and Metallurgical Bonding
Native oxides on particles and substrates hinder bonding. Impact fractures these layers, with jets aiding removal. Once achieved, fresh contact enables:
- Mechanical Interlocking: Deformed particles embed into substrate asperities, providing initial adhesion.
- Metallurgical Bonding: Atomic diffusion, dynamic recrystallization, and grain refinement form strong bonds. Interfaces often show nanocrystalline zones with high dislocation densities.
Bond strength combines these:
Mechanical components dominate in rough substrates, while metallurgical ones prevail in optimized systems.
Microstructure Evolution and Residual Stresses
Deposits exhibit low porosity (<1%), refined grains, and compressive stresses beneficial for fatigue. Dynamic recrystallization during impact creates ultra-fine structures, enhancing properties. However, anisotropy and residual stresses require management via post-treatment.
For insight, here’s a micrograph of a particle-substrate interface:
Recent studies propose oxide scales as bonding enhancers in certain systems, offering new perspectives on interface engineering.
Titomic’s Applications and Recent Developments
Titomic positions TKF for large-scale AM in defense, aerospace, shipbuilding, and energy. Examples include rapid prototyping of complex parts with superior strength and reduced lead times. In oil & gas, TKF minimizes downtime through repairs and custom components.
2025 highlights:
- Pressure Vessels: Collaboration with Northrop Grumman for high-performance vessels.
- Defense Acceleration: Selected for CRP DefenseTech Accelerator to speed supply chains.
- Powder Integration: Partnership with Metal Powder Works for advanced feedstocks.
Titomic co-developed AMS 7057 standards for aerospace certification. Their systems, like the D623, support massive builds—envision this in action:
Material and Nanomaterial Implications
TKF preserves feedstock microstructures, suiting refractory metals and composites. Nanoscale features—grain refinement, dislocation structures, and interface zones—boost strength and corrosion resistance. Research levers include powder nano-engineering for oxide control and hybrid deposits for functional coatings.
Challenges: Uniformity in large builds, porosity control, and long-term properties like fatigue. Environmentally, TKF promotes sustainability via reduced waste and energy.
Advantages and Challenges
Advantages:
- No melting: Low distortion, multi-material capability.
- High speed and scale: Up to 45 kg/h, large envelopes.
- Property retention: Near-bulk mechanics, enhanced fatigue.
Challenges:
- Velocity optimization to avoid rebound.
- Surface preparation for optimal bonding.
- Certification for critical sectors.
Conclusion
Titomic’s Kinetic Fusion exemplifies the potential of CSAM to transform manufacturing. By harnessing kinetic energy for solid-state bonding, it offers scalable, high-performance solutions amid 2025’s industry demands. Ongoing research into nanoscale mechanisms will further unlock its capabilities, paving the way for innovative materials and applications. For nanomaterials enthusiasts, TKF’s interface phenomena provide a rich arena for exploration.
Bonding Mechanisms in Cold Spray Additive Manufacturing (CSAM)
Cold Spray Additive Manufacturing (CSAM) is a solid-state deposition technique that accelerates metal or alloy particles to supersonic velocities (typically 300–1200 m/s) using a high-pressure gas stream, enabling them to bond upon impact with a substrate or previously deposited layers without melting. This process, also known as cold gas dynamic spraying, minimizes thermal distortions, oxidation, and phase changes common in melt-based additive manufacturing methods like laser powder bed fusion. Bonding in CSAM is a complex, multi-faceted phenomenon occurring at micro- and nano-scales, driven by kinetic energy conversion into plastic deformation, localized heating, and interfacial interactions. Recent 2025 reviews highlight ongoing debates and advancements in understanding these mechanisms, emphasizing their role in achieving dense, high-performance deposits.
In this overview, we’ll explore the primary bonding mechanisms, distinguish between particle-to-substrate and particle-to-particle bonding, discuss influencing factors, and highlight recent insights, including microstructure evolution and novel approaches like oxide scale fragmentation.
Overview of the CSAM Process and Bonding Fundamentals
CSAM involves injecting powder particles into a de Laval nozzle, where they are propelled by heated gas (e.g., nitrogen or helium) to achieve critical velocities for adhesion. Upon impact, the particle’s kinetic energy,
(where 
The bonding is solid-state, preserving feedstock properties and enabling multi-material or dissimilar deposits. Key mechanisms include mechanical interlocking, metallurgical bonding, and dynamic phenomena like adiabatic shear instability (ASI). These are illustrated in typical schematics of the process.
Primary Bonding Mechanisms
Bonding in CSAM is not explained by a single theory but involves interdependent processes, with dominance varying by material, parameters, and conditions.
1. Adiabatic Shear Instability (ASI) and Material Jetting
ASI is a cornerstone theory, where high strain rates cause localized thermal softening that outpaces strain hardening, forming shear bands at the interface. This leads to viscous flow and “jetting”—outward extrusion of material that disrupts surface oxides and creates fresh metal-metal contact. The local temperature rise can be approximated as:
where β≈0.9\beta \approx 0.9β≈0.9 is the heat conversion fraction, τ\tauτ shear stress, γ\gammaγ strain, ρ\rhoρ density, and cpc_pcp specific heat. ASI facilitates bonding in ductile materials like FCC metals (e.g., Al, Cu, Ni), but its necessity is debated; some studies show adhesion without clear ASI signatures.
2. Oxide Layer Disruption and Fresh Metal Contact
Native oxide films on particles and substrates act as barriers to bonding. High-velocity impact fractures or strips these layers, with jetting aiding removal. Recent 2025 research proposes enhancing bonding via controlled oxide scale fragmentation, particularly in Ti6Al4V, where strain-driven cracking exposes clean surfaces. In high-strain regions, oxides segment and disperse, enabling direct metallurgical contact, while central areas show perpendicular cracks leading to voids. Thicker oxides increase V_cr, but nano-engineering of surfaces can optimize this.
3. Mechanical Interlocking
Particles deform and embed into the substrate, creating “tooth-in-groove” features enhanced by surface roughness and asperities. This provides initial adhesion, often dominating in less-optimized systems. Studies on Cu-Al systems show mechanical components contributing most to bond strength, with metallurgical aspects requiring clean interfaces.
4. Metallurgical Bonding
Once oxide-free contact is achieved, atomic-scale bonds form through diffusion, intermixing, and dynamic recrystallization. This includes grain refinement (to <10 nm in Al), nanocrystalline zones, and even amorphization (~3 nm interfaces in Al-Mg). In dissimilar materials, intermetallics may form, but CSAM’s low heat minimizes this.
Bond strength combines these:
with mechanical interlocking often primary, but metallurgical enhancing long-term performance.
Particle-to-Substrate vs. Particle-to-Particle Bonding
- Particle-to-Substrate (Adhesive Bonding): Forms the foundation layer, primarily via ASI and mechanical embedding. Optimal at 45° impact angles, with strengths up to 250 MPa. Influenced by substrate preparation (e.g., roughness, pre-heating).
- Particle-to-Particle (Cohesive Bonding): Builds subsequent layers through similar mechanisms but with heterogeneous deformation (high strain at interfaces, low at particle caps). Leads to densification (<1% porosity) via repeated impacts. Cohesive strength is tested via standards like ASTM C633, often exceeding 77 MPa in assisted processes.
Factors Influencing Bonding
| Factor | Description | Impact on Bonding |
|---|---|---|
| Particle Velocity | Must exceed V_cr; higher velocities increase deformation and jetting. | Enhances efficiency and strength; e.g., >600 m/s for optimal adhesion. |
| Particle Size & Morphology | Smaller particles raise V_cr due to heat dissipation; irregular shapes aid interlocking. | Affects oxide content and deformation; optimal 10–50 μm. |
| Gas Temperature/Pressure | Heats particles (below melting) to reduce V_cr. | Improves ductility; e.g., helium for harder materials. |
| Material Properties | FCC metals bond best due to slip systems; BCC/HCP show higher porosity. | Ductility and stacking fault energy dictate microstructure. |
| Impact Angle & Standoff | Oblique angles promote shear; optimal standoff ensures velocity. | 45–90° for best adhesion; affects jetting. |
| Oxide Thickness | Thicker layers hinder contact; fragmentation key in new models. | Increases V_cr; nano-control enhances bonding. |
Microstructure Evolution and Recent Insights
Impacts induce high dislocation densities, dynamic recrystallization, and phase transformations (e.g., HCP to FCC in Co). Deposits exhibit refined grains, compressive residual stresses (beneficial for fatigue), and anisotropic properties. For Ti, heterogeneous microstructures with porosity arise from low ductility.
Recent advances (2025) include single-particle impact studies revealing kinetic-dominated stresses and oxide roles. A novel dual-scale model for Ti6Al4V shows strain-rate-dependent oxide fragmentation improving metallurgical bonding, validated by TEM. Hybrid processes (e.g., laser-assisted) boost strengths to 76.8 MPa. Unresolved questions involve universal theories and high-strain-rate data for simulations.
Challenges and Implications
Challenges include porosity in hard materials, residual stresses, and certification for aerospace. Post-treatments like heat treatment or HIP relieve stresses and enhance cohesion. CSAM’s eco-friendliness (low energy, minimal waste) aligns with sustainable manufacturing. For nanomaterials, interface engineering offers opportunities for tailored properties, such as wear-resistant coatings.
In summary, bonding in CSAM integrates mechanical and metallurgical processes, with ASI and oxide disruption central to success. Ongoing research refines these understandings, promising broader industrial adoption.
Oxide Scale Fragmentation in Cold Spray Bonding Mechanisms
Oxide scale fragmentation is a key phenomenon in cold spray additive manufacturing (CSAM), particularly in enhancing metallurgical bonding. In CSAM, metal particles are accelerated to high velocities and impact a substrate without melting, relying on plastic deformation for adhesion. Most metal powders, like Ti6Al4V, develop thin native oxide layers (e.g., TiO₂) during production or storage, which act as barriers to direct metal-metal contact. Traditionally, these oxides must be disrupted or removed for effective bonding, but recent research (as of 2025) has shifted focus to leveraging controlled fragmentation of these scales to improve bonding quality.
Role of Oxide Scales in Bonding
In cold spray, bonding occurs when particles exceed a critical velocity, converting kinetic energy into severe plastic deformation at strain rates up to 106−109s−1. Oxide scales (typically 5–100 nm thick) hinder this by preventing intimate contact. Conventional theories emphasize mechanisms like adiabatic shear instability (ASI), where localized heating and shear lead to material jetting that strips or disrupts oxides. However, incomplete disruption can result in residual oxide at interfaces, causing voids, weak adhesion, and reduced mechanical properties like fatigue strength.
Fragmentation refers to the strain-induced cracking, segmentation, and dispersion of these oxide layers during impact. Rather than viewing oxides solely as obstacles, emerging studies propose that controlled fragmentation can expose fresh metallic surfaces, facilitating stronger metallurgical bonds through atomic intermixing and diffusion.
Mechanism of Oxide Scale Fragmentation
The process is driven by interfacial plastic strain during particle-substrate or particle-particle impact:
- Impact and Deformation: Upon collision, the particle flattens, generating high compressive and shear stresses. The oxide scale, being brittle, experiences tensile strains from the underlying metal’s deformation.
- Strain-Driven Cracking: In high plastic strain regions (e.g., particle edges), large deformations cause the oxide to segment into small pieces and disperse, creating gaps that allow direct metal-metal contact. In contrast, the central impact region often shows perpendicular cracking, where oxides crack vertically but remain partially intact, leading to amorphous layers, voids, and weaker bonding.
- Aspect Ratio of Gaps: Bonding quality depends on the width-to-height ratio of fracture-induced gaps in the oxide. Higher ratios (influenced by deformation rate, oxide thickness, and impact velocity) promote better contact and stronger bonds. For instance, higher particle velocities increase deformation extent, enhancing fragmentation and exposing more fresh metal.
This dual behavior is modeled using multi-scale simulations (e.g., finite element methods combined with high-resolution TEM validation), showing that fragmentation is not uniform but zone-dependent. No universal equation governs fragmentation, but local temperature rises from plastic work can be approximated as:
where $( \beta )$ is the heat conversion fraction $(~0.9)$, $( \tau )$ is shear stress, $( \gamma )$ is strain, $( \rho )$ is density, and $( c_p )$ is specific heat. This heating softens the metal, amplifying strain on the oxide.
Here’s a diagram illustrating oxide scale fragmentation during impact:
Reconstructed Oxide Scales for Controlled Fragmentation
A novel approach involves reconstructing the oxide scale on powders to make it more prone to fragmentation. For Ti6Al4V, treatments like acid etching create a loose, friable, and rough oxide layer (20–60 nm thick) with increased lower-valence oxides (e.g., Ti₂O₃). This reconstructed scale is brittle and uneven, promoting controlled fracture and peeling during impact, which reduces the oxide barrier and exposes fresh surfaces.
- Fracture Behavior: The friable structure leads to easier segmentation and dispersion, minimizing residual oxide at interfaces. Atomic-resolution STEM shows reduced oxide thickness and improved metallic continuity.
- Bonding Improvement: This results in up to 16% higher bonding strength, better coating density, and enhanced performance in applications like aerospace. Factors like surface roughness (increased Sa values) and specific surface area amplify the effect.
This method shifts from oxide removal (e.g., via reduction) to engineering the scale for optimal fracture, addressing challenges in ductile materials like titanium alloys where natural oxides are dense and resistant.
Another visual representation of oxide behavior in reconstructed scales:
Implications and Challenges
Fragmentation enhances metallurgical bonding by increasing bonded areas and quality, leading to denser deposits with low porosity (<1%) and superior mechanical properties. It’s particularly relevant for hard-to-bond materials like titanium alloys. However, challenges include controlling oxide thickness (thicker scales raise critical velocity) and ensuring uniform fragmentation across impacts.
Ongoing research uses simulations and microscopy to optimize parameters like velocity, gas temperature, and powder pretreatment. This approach not only improves CSAM efficiency but also expands its use in high-performance coatings and repairs.
Notes on Figure Use and Licensing